Easier custom regex flags and tests

[aolieman]

This adds tests for the use of custom regex flags. While writing the tests, I encountered some problems monkeypatching the config neatly, so I refactored this mechanism.

The tests also uncovered that the type check in Expression.findall() was problematic for cross-version compatibility. This could be overcome by using past.builtins.basestring, which unfortunately is not compatible with py3.2. Due to the lack of unicode string marker support in py>=3.0,<3.3, it seems practically impossible to maintain support for these versions while allowing custom regex flags.

[andychase]

This look good, I'll merge this.

I'm going to do a rebase though afterward-- instead of loosing python 3.2 support I'm go to rebase this to detect strings with:

if hasattr(match, 'strip'):

Instead of

if isinstance(match, basestring):

The former keeps Python 3.2 support and doesn't require an extra library.

[aolieman]

Alright, good catch! Any idea as to when the new release will show up on PyPI?

[andychase]

I did a final review of all the code, added some notes and released just now!