move the class files out of the plugin dir

On some new versions of vim these files were being loaded before the
main NERD_tree.vim which was causing errors as dependencies werent
loaded in time. Move the classes into lib - so vim wont try to load them
until we tell it

autoload/nerdtree.vim

@@ -227,6 +227,19 @@ function! nerdtree#invokeKeyMap(key)
     call g:NERDTreeKeyMap.Invoke(a:key)
 endfunction
 
+" FUNCTION: nerdtree#loadClassFiles() {{{2
+function! nerdtree#loadClassFiles()
+    runtime lib/nerdtree/path.vim
+    runtime lib/nerdtree/menu_controller.vim
+    runtime lib/nerdtree/menu_item.vim
+    runtime lib/nerdtree/key_map.vim
+    runtime lib/nerdtree/bookmark.vim
+    runtime lib/nerdtree/tree_file_node.vim
+    runtime lib/nerdtree/tree_dir_node.vim
+    runtime lib/nerdtree/opener.vim
+    runtime lib/nerdtree/creator.vim
+endfunction
+
 " FUNCTION: nerdtree#postSourceActions() {{{2
 function! nerdtree#postSourceActions()
     call g:NERDTreeBookmark.CacheBookmarks(0)

plugin/NERD_tree.vim

@@ -136,15 +136,7 @@ call s:initVariable("g:NERDTreeMapUpdirKeepOpen", "U")
 call s:initVariable("g:NERDTreeMapCWD", "CD")
 
 "SECTION: Load class files{{{2
-runtime plugin/nerdtree/path.vim
-runtime plugin/nerdtree/menu_controller.vim
-runtime plugin/nerdtree/menu_item.vim
-runtime plugin/nerdtree/key_map.vim
-runtime plugin/nerdtree/bookmark.vim
-runtime plugin/nerdtree/tree_file_node.vim
-runtime plugin/nerdtree/tree_dir_node.vim
-runtime plugin/nerdtree/opener.vim
-runtime plugin/nerdtree/creator.vim
+call nerdtree#loadClassFiles()
 
 " SECTION: Commands {{{1
 "============================================================