Error handling for notebooks with invalid format
Undo change made to example nb for testing
Changed error message
Flake8 style fixes
Added/fixed error handling
Flip merge arrow buttons to undo a merge choice.

Squashed commit of the following:

commit 495c4b5a49b2f42813ee52f88bace0e22c437560
Merge: 5483909 efec3d0
Author: Tavish Armstrong <tavisharmstrong@gmail.com>
Date:   Tue Mar 4 20:37:20 2014 -0500

    Fix merge conflict.

commit 5483909ea5512b2718b10f55946fbcd34d37f911
Author: bsplay <bsplay@github.com>
Date:   Sat Mar 1 14:09:31 2014 -0500

    making jshint happy

commit 31f58e711dce98055df59732d61ae45470671df7
Author: bsplay <bsplay@github.com>
Date:   Sat Mar 1 13:55:39 2014 -0500

    drag/drop changes arrow

commit af8f67db97285cd6f72aa09e86a3fa8bbffdf6bd
Author: bsplay <bsplay@gmail.com>
Date:   Fri Feb 28 13:06:46 2014 -0500

    undo arrow
s/tabs/spaces/ in drag_drop.js
Use swc notebooks as test diff notebooks
Add actual diff of IPythonReviewTime.ipynb to example-notebooks folder
Make diff lines monospace/whitespace-significant
Merge pull request #171 from tarmstrong/diff-line-style-fixes

Diff line style fixes & extra notebooks for diff testing script
Add note on current stability :-)
Changed when error handling messages appear and fixed code so that we don't try and send the notebook to the flask after the format is invalid
Fix notebook should not be sent to flask if invalid type
Add --check argument for profiling/testing purposes.
Run nbdiff and nbmerge commands on travis.
Fix test-merge script.
Configure git in travis build so the scripts work.
Remove python 2.6 from build.
Merge pull request #172 from tarmstrong/test-commands-travis

Run nbdiff/nbmerge commands in travis build