Fix bug where use of .ix[tuple(...)]=x fails to correctly check out of b...
...ounds index for columns. This is a regression as it used to work in pandas 0.12.0. The code incorrectly checks the column index against the len() of the dataframe to see if it is in bounds not against the number of columns. Have added 2 tests with non-square dataframes to test that the fix works.

gr8 pls add a release notes entry refing this PR as I don't think this has an issue associated?
 perfect...just need to rebase (conflict in release notes)...

`git rebase -i upstream/master`

fixup and force push...then can merge
 thanks!
