Fixed filename of distutils-scripts on windows. Fixes #52

Adding missing *.test files to manifest, needed for manuel tests

Merging buildout-versions' functionality into buildout

Unlike the console-script entrypoint scripts, the distutils
scripts didn't get a -script.py appended to their name on
windows. This is now fixed.

As discussed on the mailinglist: better to have python version checking
as a separate buildout option instead of hidden in the [versions] part.
And... the python version checking itself needs to be more robust.
sys.version is too long, minor/major needs explicit checking.

Drop trove classifiers for Python 2.4 and 2.5

I guess this was why the pull request wasn't build.

An 'update-versions-file' option points at a file you want updated.

I cannot handily use print_ from buildout.py as I get a circular import that way.

The Python package index is case-insensitive. Both
http://pypi.python.org/simple/Django/ and
http://pypi.python.org/simple/dJaNgO/ work. And distributions aren't always
naming themselves consistently case-wise. So all version names are normalized
and case differences won't impact the pinning.

Possible problem: distribute is also reported as have-to-pick. So I
pinned it to 0.6.34, the current value. It might bite us later on, I fear.
I don't know enough about the setup to be sure.

Included: functionality (copy/pasted from buildout-versions) to
actually record and print the picked versions. For this, two new
class-level attributes on the Installer are added.

TODO: testing whether the printing of what required what also
works.

The [versions] section is checked for a 'python' key.
Functionality copied from buildout-versions.
Includes documentation and tests.

README.rst claims only 2.6, 2.7, 3.2 and 3.3 are supported.

Everything is in place now for actually implementing it.

I need to go through buildout-versions' finish() method, still.