Do not remove an existing egg.

After a dist is fetched and put into its final place, compile its
python files.  No longer wait with compiling until all dists are in
place.

This avoids calling redo_pyc at the same time by two parallel buildouts.
It might not be so bad, but it seems better (and faster) to avoid it.

See discussion at https://github.com/buildout/buildout/issues/307

When installing an egg to a location that already exists, keep the
current location (directory or file).

This can only happen when the location at first did not exist and this
changed during the buildout run.  We used to remove the previous
location, but this could cause problems when running two buildouts at
the same time, when they try to install the same new egg.

Fixes #307.

In the tests, filter out an invisible control character.

This avoids invisible control characters popping up in some terminals, like `xterm`.

Note that this may affect tests by buildout recipes.

Fixed bootstrap test for newer setuptools.

setuptools used to say this:

    No local packages or download links found for zc.buildout==UNKNOWN

Since setuptools 25.1.0 it says this:

    No local packages or working download links found for zc.buildout==UNKNOWN

See also https://github.com/pypa/setuptools/pull/609/files

Fix typo

No python 3.3 and newer versions of the other pythons

Remove Python 2.6 and Python 3.2 support

Refs #297

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Simple Fix for 'Extending sections (macros)' in combination with += and -=.

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It was originally called 'path'

Turn proposed patch into a pull request.

https://github.com/buildout/buildout/issues/257#issuecomment-159423299

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Nicer version constraint logging + better requirement conflict info logging

The tests fail to run due to the deprecation warnings, so I stripped 3.2 out of travis.

Added 3.5 instead as that's the most modern version.

"dist" can be a PathMetaData instance, req.key is nicer. The latter has a .lower()...

Before you'd get a simple output like:

    Installing django.
    While:
      Installing django.
    Error: The requirement ('Django>=1.7') is not allowed by your [versions] constraint (1.6.6)

... which would mean you'd have to grep in all your requirements'
sub-requirements which package actually requires the offending "django>=1.7"

With this change you'll get a much more helpful output right before the error:

    Installing django.
    version and requirements information containing django:
      [versions] constraint on django: 1.6.6
      Base installation request: 'sso', 'djangorecipe'
      Requirement of djangorecipe==1.10: Django
      Requirement of djangorecipe==1.10: zc.recipe.egg
      Requirement of djangorecipe==1.10: zc.buildout
      Requirement of sso: django-nose
      Requirement of sso: django-mama-cas
      Requirement of sso: django-debug-toolbar
      Requirement of sso: django-auth-ldap
      Requirement of sso: Django<1.7,>=1.4.2
      Requirement of lizard-auth-server: django-nose
      Requirement of lizard-auth-server: django-extensions
      Requirement of lizard-auth-server: Django<1.7,>=1.6
      Requirement of django-nose: Django>=1.2
      Requirement of django-nose: nose>=1.2.1
      Requirement of django-mama-cas: requests==1.1.0
      Requirement of django-debug-toolbar: sqlparse
      Requirement of django-debug-toolbar: Django>=1.7
      Requirement of django-auth-ldap: python-ldap>=2.0
      Requirement of django-auth-ldap: django>=1.1
      Requirement of translations: Django>=1.4
      Requirement of django-extensions: six>=1.2
    While:
      Installing django.
    Error: The requirement ('Django>=1.7') is not allowed by your [versions] constraint (1.6.6)

This makes it much easier to spot the cause (in this case
django-debug-toolbar).

There *are* some unrelated packages in here because I'm doing a textual
comparison. The advantage is that it is very robust. And extracting the right
package name from requirements without messing things up is harder to get
right and takes more code.

- Adjusted the now-clearer error.
- Removed error log message as that's now in the actual error message

Previously:

    The constraint, 1.6.6, is not consistent with the requirement, 'Django>=1.7'.
    While:
      Updating django.
    Error: Bad constraint 1.6.6 Django>=1.7

Now:

    While:
      Installing django.
    Error: The requirement ('Django>=1.7') is not allowed by your [versions] constraint (1.6.6)

The original message said "bad constraint". No, the constraint is not
necessarily bad. It only conflicts with some other package's requirement.

The new message tells you that "constraint" means "your own [versions]
list".

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