Adding in vim patch for OSX 10.9 to allow building

Currently vim hasn't successfully built on Mavericks since a few weeks ago. This patch fixes that issue.

Described in more detail on [this vim-dev thread](https://groups.google.com/forum/#!msg/vim_dev/YHo51sA46fU/cybmVD3v3SkJ).

I've mirrored a copy of the diff on a versioned Gist because the version pasted on the thread has some sort of header that doesn't merge cleanly in Homebrew.

Tested and works on my local Mavericks.