Refactored execute permission into one spot.

A fixed (0755) execute permission is used in two places, I refactored it into
one method. Bonus: this makes it easy to test the fix proposed in
https://github.com/buildout/buildout/pull/18
Added test whether scripts are made executable.

Note: includes if/else for windows.
Uses http://docs.python.org/2/library/os#os.access
Using distribute's way of chmod +x.

os.umask is a bit weird in that it *does* return the current umask,
but it has a required argument that it immediately sets as the new umask...
Weird. Distribute solves that by assigning a dummy value and re-setting
the umask to the original value.

The matching test verifies that it actually works.

Note that I use python 2.6+'s octal notation: 0o755.
Buildout 2 doesn't support python 2.5 anymore, iirc, so that's fine.
PEP8 changes for bootstrap.py

I changed a few things to allow for better pep8 compatability.
Merge pull request #77 from rvanlaar/patch-1

PEP8 changes for bootstrap.py
Merge pull request #75 from reinout/use-umask

Use umask when doing "chmod +x". Improved version of pull request #18
skip umask test on windows
Awful hack to to temporarily get around a test bug (test depends on
the current distribute version).
Made tests independent of distribute version.

Replaced the fixed distribute version number with the currently valid one by
just asking for the current version and inserting that in the various spots we
need it in this testfile
Merge pull request #78 from reinout/reinout-distribute-version-test-fix

Made tests independent of distribute version number
prep for release (and provoke travis)
Merge remote-tracking branch 'buildout/master' into header_expressions
Use more explicit variable names