Allow joins between MultiIndexes and normal Indexes to make use of common keys
Hi not sure the best way to describe this but this stackoverflow question explains the problem nicely: http://stackoverflow.com/questions/14149156/merge-multi-indexed-with-single-indexed-data-frames-in-pandas

Would be nice to be able to do this without the awkward reindex. Thanks again for a great project.

Currently on version 0.10.1
