Redraw screen when using MMBackend gotoTab:withPath:

Fixes issue where MMVimView is not updated when using MMVimController
method gotoBufferWithUrl: (proxied to MMBackend openWindowWithUrl:) and
the url specifies a file that is open in an existing tab.
Merge pull request #9 from dnerdy/tab-redraw-screen

Redraw screen when using MMBackend gotoTab:withPath: