Modified RowSet __repr__ to use %r instead of %s.

This is required to ensure __repr__ escapes unicode characters as a string rather than returning a unicode object.
Added __getitem__ to TableSet which allows getting a RowSet by name
Added a test file and unit test for previous commit 7ce2f4c98e1b72c30bd0cf48c773d20e4d7a20c3
Removed use of TestCase.assertIsInstance for python-2.6 compatibility.
Merge remote-tracking branch 'scraperwiki/master'
Style