Vundle plugin now works with submodules.

If you are using a submodule, ~/.vim/bundle/vundle/.git is a file,
not a directory. So I changed the test for that.

plugins/vundle/vundle.plugin.zsh

@@ -4,7 +4,7 @@ function vundle-init () {
     mkdir -p ~/.vim/bundle/vundle/
   fi
 
-  if [ ! -d ~/.vim/bundle/vundle/.git/ ]
+  if [ ! -d ~/.vim/bundle/vundle/.git ] && [ ! -f ~/.vim/bundle/vundle/.git ]
   then
     git clone http://github.com/gmarik/vundle.git ~/.vim/bundle/vundle
     echo "\n\tRead about vim configuration for vundle at https://github.com/gmarik/vundle\n"