fix flag rendering for cascading dirs

Use the innermost dirs flags only. Previously each dirs flags were
rendered inline i.e.

    [x]dir1/[y]dir2/[z]dir3/

This looked bad and broke the UI. Now we only render the flags for dir3
- and render them on the left side of the cascade.

Not sure if this is ultimately the right decision - but will do for now.

lib/nerdtree/path.vim

@@ -40,9 +40,7 @@ endfunction
 
 "FUNCTION: Path.cacheDisplayString() {{{1
 function! s:Path.cacheDisplayString() abort
-    let self.cachedDisplayString = self.flagSet.renderToString()
-
-    let self.cachedDisplayString .= self.getLastPathComponent(1)
+    let self.cachedDisplayString = self.getLastPathComponent(1)
 
     if self.isExecutable
         let self.cachedDisplayString = self.cachedDisplayString . '*'

lib/nerdtree/tree_dir_node.vim

@@ -84,7 +84,9 @@ function! s:TreeDirNode.displayString()
 
     let sym = cascade[-1].isOpen ? g:NERDTreeDirArrowCollapsible : g:NERDTreeDirArrowExpandable
 
-    return sym . ' ' . rv
+    let flags = cascade[-1].path.flagSet.renderToString()
+
+    return sym . ' ' . flags . rv
 endfunction
 
 "FUNCTION: TreeDirNode.findNode(path) {{{1

lib/nerdtree/tree_file_node.vim

@@ -83,7 +83,7 @@ endfunction
 "Return:
 "a string that can be used in the view to represent this node
 function! s:TreeFileNode.displayString()
-    return self.path.displayString()
+    return self.path.flagSet.renderToString() . self.path.displayString()
 endfunction
 
 "FUNCTION: TreeFileNode.equals(treenode) {{{1