This allows a recipe building python to add custom extra-path

This commit contain modifications that allow ocropy and scipy to be
installed as eggs. Extra ld_path are added to python to allow the former
to run scipy (that needs libstdc++) inside testnodes.

This commit add component needed for Optical Character recognition:
ocropy and its dependancies

The Ocropy egg on Pypi is empty, so this component have to be built from
source. The default neural network model is downloaded from the author
website and installed in python2.7/share/ocropus.

The patch is here for to different thing: one is adding an
OCROPY_MODEL_PATH to be able to specify the position of models, the
other is importing for the first time a module that compile C code from
python, allowing us to have the static library built before runtime and
preventing us from using gcc through zope.

More models are available here:
https://github.com/tmbdev/ocropy/wiki/Models

Makes it easier to deploy a functional replication setup.

They closed, and downloads get redirected to a wiki page.

Stop breaking this tool for everyone developping on slapos.

  Apache verbose way too much with LogLevel info

It was not working with wrappers to work around shebang length limitation.

https://bitbucket.org/sirex/rubygemsrecipe/issues/9/gem-shebang-line-length-limitation

  Allow set software-root via parameters allow the webrunner inside a erp5testnode,
  recover the the previous builds from previous resilient tests, and only update (instead build from scratch)
  This is a typical usage on the webrunner (keep updating SR), so there is no
  problem on use this approach on erp5testnode tests.

Use the same exclude patterns (receiving end may want to exclude a file set
different from the time backup was exported, or may have a different set of
buildout-managed files which would be dangerous and misleading to
overwrite).

Do not apply exclusions to unrelated paths ("project", "proxy.db" and
"etc").
Simplify global exclusion file generation.
Add support for absolute and partition-relative exclusion paths
(previously, only partition-relative were supported).
Pipe exclusion file to rsync, to avoid an intermediate disk write.
Remove some directory prefix duplication by using PWD-relative paths
(except in one place, for runner-import.sh.jinja2 comparison).

So avoid spawning "cat" only for this.
Also, variable expansion quoting.

More similar changes will come later as part of larger changes.
Also, fail if
  cd "$backup_directory"
fails, as it is supposed to exist by that point.

Imperfect: single-quote escaping would be good. But this at least makes
it significantly harder to accidentally end up outside variable assignment.
Users of these values will be added in a later commit.