Place swapfiles under a single directory

Designates ~/.vimswp (%USERPROFILE%\Local Settings\Temp in Win32) as the
place to hold vim swap files, preserving path info to avoid collisions
(:help directory). This also lets us avoid disabling swapfiles for
directories where they shouldn't be created (e.g. gvfs, Dropbox)
Update Vundle to commit 5dd478e1