Use :mode only in neovim. MacVim still needs to use :redraw! (#1019)

* Use :mode only in neovim. MacVim still needs to use :redraw!

* Make nerdtree#redraw do both redraw and redraw! based on a parameter.

* Make bang a required parameter.

* Replace all redraw statments with call nerdtree#redraw function calls.

* Update version in change log.

autoload/nerdtree.vim

@@ -22,8 +22,24 @@ endfunction
 " SECTION: General Functions {{{1
 "============================================================
 
-function! nerdtree#slash()
+"FUNCTION: nerdtree#redraw(bang)
+" Redraws the screen (Neovim uses the mode statement). If bang is TRUE, use
+" redraw! instead of redraw.
+function! nerdtree#redraw(bang)
+    if has('nvim')
+        mode
+    else
+        if a:bang
+            redraw!
+        else
+            redraw
+        endif
+    endif
+endfunction
 
+"FUNCTION: nerdtree#slash()
+" Returns the directory separator based on OS and &shellslash
+function! nerdtree#slash()
     if nerdtree#runningWindows()
         if exists('+shellslash') && &shellslash
             return '/'
@@ -216,7 +232,7 @@ endfunction
 "Args:
 "msg: the message to echo
 function! nerdtree#echo(msg)
-    redraw
+    call nerdtree#redraw(0)
     echomsg empty(a:msg) ? "" : ("NERDTree: " . a:msg)
 endfunction