Prevent unneeded tree creation in :NERDTreeToggle[VCS] <path> (#1101)

* Don't recreate the NERDTree if its root is the same as being requested.

* Use single quotes per Vint's style recommendation.

* Update version number in changelog.

* Use a simpler method of getting the NERDTree root path.

* Remove variable. Just compare agains the function call's result.

lib/nerdtree/creator.vim

@@ -366,7 +366,7 @@ function! s:Creator.toggleTabTree(dir)
     if g:NERDTree.ExistsForTab()
         if !g:NERDTree.IsOpen()
             call self._createTreeWin()
-            if !empty(a:dir)
+            if !empty(a:dir) && a:dir !=# b:NERDTree.root.path.str()
                 call self.createTabTree(a:dir)
             elseif !&hidden
                 call b:NERDTree.render()