misc/vim: Added filetype settings for comments.

This basic Vim ftplugin sets the 'comments' and 'commentstring'
settings to sensible values. Future filetype settings for Go
would go in the same file.
The ftplugin was added as misc/vim/ftplugin/go/go.vim, this way
the installation instructions in readme.txt remain valid.
Fixes #5715.

R=dsymonds
CC=gobot, golang-dev
https://golang.org/cl/10323043

misc/vim/ftplugin/go.vim

+" Copyright 2013 The Go Authors. All rights reserved.
+" Use of this source code is governed by a BSD-style
+" license that can be found in the LICENSE file.
+"
+" go.vim: Vim filetype plugin for Go.
+
+if exists("b:did_ftplugin")
+    finish
+endif
+let b:did_ftplugin = 1
+
+setlocal comments=s1:/*,mb:*,ex:*/,://
+setlocal commentstring=//\ %s
+
+let b:undo_ftplugin = "setl com< cms<"
+
+" vim:ts=4:sw=4:et

misc/vim/readme.txt

@@ -47,9 +47,10 @@ Vim filetype plugins
 To install one of the available filetype plugins:
 
   1. Same as 1 above.
-  2. Copy or link one or more plugins from ftplugin/go/*.vim to the
-     Go-specific ftplugin directory underneath your vim runtime directory
-     (normally $HOME/.vim/ftplugin/go/*.vim).
+  2. Copy or link ftplugin/go.vim to the ftplugin directory underneath your vim
+     runtime directory (normally $HOME/.vim/ftplugin). Copy or link one or more
+     additional plugins from ftplugin/go/*.vim to the Go-specific subdirectory
+     in the same place ($HOME/.vim/ftplugin/go/*.vim).
   3. Add the following line to your .vimrc file (normally $HOME/.vimrc):
 
      filetype plugin on