misc/emacs: Enable compilation-mode for gofmt error buffer before displaying it.

Some packages, like popwin.el, change display behaviour based on
the buffer's mode, so we should enable compilation-mode before
displaying the buffer.

R=golang-dev, bradfitz
CC=golang-dev
https://golang.org/cl/8155043

misc/emacs/go-mode.el

@@ -565,8 +565,8 @@ buffer."
     (insert "gofmt errors:\n")
     (while (search-forward-regexp (concat "^\\(" (regexp-quote tmpfile) "\\):") nil t)
       (replace-match (file-name-nondirectory filename) t t nil 1))
-    (display-buffer errbuf)
-    (compilation-mode)))
+    (compilation-mode)
+    (display-buffer errbuf)))
 
 ;;;###autoload
 (defun gofmt-before-save ()