Add OverflowError to the exception list during column type conversion
Update CHANGES.rst
Fall through to string instead of float and emit warning
Update test of overflow condition
Update CHANGES.rst
Fix overflow test to work on numpy 1.5
Add known issue that overflowing ints get cast to float in ascii.read for numpy 1.5
Merge pull request #2234 from taldcroft/catch-overflow

In io.ascii, fall back to string if integers are too large