Remove AddDefaultGroupToSortOrder check from startup.

The call to AddDefaultGroupToSortOrder in NERD_tree.vim is redundant
because it's also done every time sortChildren is called. And since the
check is done only once, there's no need for a function either.
sortChildren now just contains the needed if statement.

lib/nerdtree/tree_dir_node.vim

@@ -607,7 +607,9 @@ endfunction
 " FUNCTION: TreeDirNode.sortChildren() {{{1
 " Sort "self.children" by alphabetical order and directory priority.
 function! s:TreeDirNode.sortChildren()
-    call AddDefaultGroupToSortOrder()
+    if count(g:NERDTreeSortOrder, '*') < 1
+        call add(g:NERDTreeSortOrder, '*')
+    endif
     let CompareFunc = function("nerdtree#compareNodesBySortKey")
     call sort(self.children, CompareFunc)
 endfunction

plugin/NERD_tree.vim

@@ -24,15 +24,6 @@ let loaded_nerd_tree = 1
 let s:old_cpo = &cpo
 set cpo&vim
 
-"Function: AddDefaultGroupToSortOrder() function {{{2
-"This function adds the default grouping '*' to the sort sequence if it's not
-"already in the list.
-function! AddDefaultGroupToSortOrder()
-    if count(g:NERDTreeSortOrder, '*') < 1
-        call add(g:NERDTreeSortOrder, '*')
-    endif
-endfunction
-
 "Function: s:initVariable() function {{{2
 "This function is used to initialise a given variable to a given value. The
 "variable is only initialised if it does not exist prior
@@ -90,8 +81,6 @@ call s:initVariable("g:NERDTreeCascadeSingleChildDir", 1)
 
 if !exists("g:NERDTreeSortOrder")
     let g:NERDTreeSortOrder = ['\/$', '*', '\.swp$',  '\.bak$', '\~$']
-else
-    call AddDefaultGroupToSortOrder()
 endif
 
 call s:initVariable("g:NERDTreeGlyphReadOnly", "RO")