change NERDTree to exit after opening a file, also add fugitive vim plugin

Since our <leader>d shortcut now works, the NERDTree exit makes sense.
Also, let's learn how to use fugitive.

.gitmodules

@@ -28,3 +28,6 @@
 [submodule "vim/bundle/surround"]
 	path = vim/bundle/surround
 	url = https://github.com/tpope/vim-surround
+[submodule "vim/bundle/fugitive"]
+	path = vim/bundle/fugitive
+	url = git://github.com/tpope/vim-fugitive.git

vim/bundle/fugitive

@@ -0,0 +1 @@
+Subproject commit 5298448e8895e70c401bbf394b8aa948135dd261

vim/vimrc

@@ -164,7 +164,7 @@ nmap <silent> <leader>s    :set scrollbind! scrollbind?<CR>
 " Toggle mouse support.
 nnoremap <leader>m         :call ToggleMouse()<CR>
 
-" Toggle NERDTree instead of the normal dir browser... Doesn't seem to work yet
+" Toggle NERDTree file browser
 nnoremap <silent> <leader>d    :NERDTreeToggle<CR>
 
 " Toggle Commenting out lines with NERDCommenter
@@ -212,7 +212,7 @@ nnoremap <silent> <expr> $ ScreenMovement("$")
 "" Plugin options
 """"""""""""""""""""""""""""""""""""""""""""""""""""""""
 
-" let g:NERDTreeQuitOnOpen = 1
+ let g:NERDTreeQuitOnOpen = 1
 
 " Having problems showing NERDTree arrows in OS X
 if s:uname == "Darwin"