Added test: future and docstring in distutils scripts
Distutils script: supporting future and docstrings.

Fixes #102

Distutils scripts can contain quite a lot of code. Up till now,
only a encoding hint was detected and placed at the top above
our 'import sys' and 'sys.path=' stuff.

Now we look for the first non-__future__ import line and place our
sys.path statement above that line. This makes sure the encoding hint,
the module docstring and the future imports are all above our code,
as should be.

There might be corner cases, but at least this fixes a couple of
common problems.
Added test for multiple imports in distutils script.

This exposes a bug.
Breaking after finding first import line.

Fixes a bug with multiple import lines. We want to insert ourselves after the
*first* found import line, not the last one...

Also simplified an if/else for when there's no import statement at all.
Restored blank line
Merge branch 'reinout-future-import-scripts' of https://github.com/reinout/buildout into reinout-reinout-future-import-scripts
Changelog for PR #112.