Teach GitLab not only to merge changes from a merge-request, but also to
apply patches posted to merge-request in a way like `git am` would do -
without merge commit and directly on top of current branch. Which way to
go is selected by user in web UI, and apply patches is the first option.

There are 3 cases:

- only 1 commit is present in MR -> the only available option is to
  apply that single commit as one patch without a merge

  ( There is no need for merge commit in this case at all: information
    about user who applied the patch goes to "Committer" field in resultant
    commit. Avoiding 1 merge per 1 patch results in cleaner history )

  It is also possible to review patch description directly in web UI,
  before doing the actual application, and correct / amend it as needed.

- several commits are present in MR:

  * it is possible to apply the patches directly on top of current
    branch. Again information about who applied what goes to "Committer"
    field.

  * it is possible to merge MR changes with making a merge commit.

    This variant is useful, when patches from a MR do several logical
    steps to reach one goal, and MR description contain cover letter for
    whole patch series.

    in this case original commits stay untouched and resulting merge
    will contain MR author as author, user who accepted MR as committer,
    and cover letter as merge commit message.

    NOTE we avoid useless "Merge branch X into Y" in merge message, and
        just put MR title into merge subject and MR description into merge
        description.

        This way it is more logical with more important information in
        merge subject and thus e.g. more handy to oversee what a merge brings,
        just by it subject, e.g. via looking at updates via

            gitk --first-parent ...

        or via web.

NOTE for pre-generated references to merge-request we now use full MR
    URL, instead of !<MR-n>. Full URLs work everywhere, not only on
    original site where MR was created, or even only in original repo
    and not its fork on the same site.

TODO detect whether request comes from China and only then show ICP (?).

We show in small font size the same info that is shown on sign_in page:

    "GitLab Nexedi Edition", "About GitLab" and "About Nexedi"

This is good to have and hereby-introduced about-footer area will be
also used in the next patch for ICP too.

XXX placement of .about-footer to be near bottom is done not very
correctly.

Like Omnibus, SlapOS version does not have init script - nothing to
check here.

This is handy for monitoring tools, which could e.g. periodically call check
tasks and instead of parsing output, rely on exit code.

The way we detect if something failed is via hooking into String#red, and if
anything was ever printed in red - that's an error.

The default was switched to HTTP in the previous patch, but let's completely
remove SSH option - we support only HTTP for git fetch/push.

Both fetch and push are possible over https, which is selected by http if
gitlab was configured to use https in external url.

This way to reduce security vectors and possible ways to interact with gitlab
we use https only without ssh at all.

= GitLab Community Edition + Nexedi patches

Ensure logged-out users can't see private refs

https://gitlab.com/gitlab-org/gitlab-ce/issues/18033

I'm still not sure what to do about the CHANGELOG on security issues - should I add to a patch release? This issue was assigned to 8.10.

See merge request !1974
(cherry picked from commit 3a6ebb1f)

Fix privilege escalation issue with OAuth external users

Related to https://gitlab.com/gitlab-org/gitlab-ce/issues/19312

This MR fixes a privilege escalation issue, where manually set external users would be reverted back to internal users if they logged in via OAuth and that provider was not in the `external_providers` list.

/cc @douwe

See merge request !1975
(cherry picked from commit 5e6342b7)

Fix visibility of snippets when searching

Fixes https://gitlab.com/gitlab-org/gitlab-ce/issues/18997

See merge request !1972
(cherry picked from commit 8a197c15)

Update omniauth-saml to 1.6.0 to address a security vulnerability in ruby-saml

Updates `omniauth-saml` to bring in the new `ruby-saml` dependency that addresses [CVE-2016-5697](https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2016-5697)

Fixes #19206

See merge request !4951
(cherry picked from commit c3a8b252)

Only show notes through JSON on confidential issues that the user has access to

Fixes https://gitlab.com/gitlab-org/gitlab-ce/issues/18535

See merge request !1970

Forbid scripting for wiki files

Wiki files (not pages - files in the repo) are just sent to the browser
with whatever content-type the mime_types gem assigns to them based on
their extension. As this is from the same domain as the GitLab
application, this is an XSS vulnerability.

Set a CSP forbidding all sources for scripting, CSS, XHR, etc. on these
files.

Fixes https://gitlab.com/gitlab-org/gitlab-ce/issues/17298.

See merge request !1969

Remove 'unscoped' from project builds selection

This is a fix for this security bug: https://gitlab.com/gitlab-org/gitlab-ce/issues/18188

/cc @kamil @grzegorz @stanhu

See merge request !1968

fix typo making gitlab.com importing to fail

Fixes https://gitlab.com/gitlab-org/gitlab-ee/issues/565

See merge request !4181

Use the relative url prefix for links in Wiki

Retry of gitlab-org/gitlab-ce!4026

@rymai !4050 solved all other problems how it looks like. I [tested](https://gitlab.com/artem-forks/gitlab-ce/commit/ff01eca7b559efa7cacf3412aa01cd8ae8a6db7e/builds) this with ruby22

Fixes #17071 



See merge request !4131

Create import data in service and fix timing issues when scheduling job

Fixes https://gitlab.com/gitlab-org/gitlab-ce/issues/17401

Fixes https://gitlab.com/gitlab-org/gitlab-ce/issues/17376

See merge request !4106

Fix an issue when filtering merge requests with more than one label

Fixes #15529.

See merge request !3886

Fix build notification on merge request page change even if the build status didn't change

## What does this MR do?
This MR contains a bugfix for #17357 which was introduced by !3998. The notification are now only shown on status changes, and not when switching between different merge requests.

## Are there points in the code the reviewer needs to double check?
Check implementation

## Why was this MR needed?
Because auf a bug introduced in !3998.

## What are the relevant issue numbers?
#17357

Closes #17357

See merge request !4086

Relative Links in the Wiki Are Broken

- [ ] #16568 (!4050) Relative links in wiki are broken
    - [x] Investigate issue

  
    - [x] Implementation / Fix

        - [x] Write (failing) tests for `WikiLinkFilter`
        - [x] Link to `./bar` should either get rewritten correctly or left alone
        - [x] Link to `./bar.md` should maybe get rewritten correctly (is left alone currently)
        - [x] Link to `bar.md` should get rewritten correctly


            - [x] Check if this indeed a bug

    - [x] Make sure CI is green
    - [x] Assign to endboss

    - [x] Wait for review

    - [x] Implement review feedback
    - [ ] Wait for merge


See merge request !4050

This MR never made it into 8.7.4.

[ci skip]

This reverts commit d1ba0986.

[ci skip]

Use a case-insensitive check to compare URI schemes

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/17299

See merge request !1965