Add tests for subclassing validators (#25).

Also fix a small issue with subclassing compound validators.
Better naming for the private overridable methods.
Enable deprecation warnings in tests in Python 2.7.

This also revealed a deprecated call to cgi.parse_qsl.
Fix line endings
Merge pull request 28
Check out OS specific script files with proper line endings.
Cleaner imports.
Consistently use unittest for all validator tests.
Remove spurious assert statement.
Use iterator methods on dicts where possible.
Run 2to3 when building Formencode.

Make test package a subpackage.
python setup.py nosetests now works properly.
Some adaptions for Python 3.
Add important option for Python 3 doctests.
Make test for deprecation warnings work with Python 3.
Small fix in test_htmlfill.
Adapt doctest output checker for Python 3.
More adaptions for Python 3.