git-blame.el: Add (require 'format-spec)

c5022f5 (git-blame.el: Change how blame information is shown,
2009-09-29) taught the "M-x git-blame" mode to format its output
in a more interesting way, making use of the format-spec function.

format-spec is included in Emacs 23 and is a useful function.
Older emacsen can get it from Gnus.  In all emacsen, we need
to 'require it before use to avoid warnings:

 git-blame.el:483:1:Warning: the function `format-spec' is not known to be
     defined.

Reported-by: Sergei Organov <osv@javad.com>
Reported-by: Kevin Ryde <user42@zip.com.au>
Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

contrib/emacs/git-blame.el

@@ -79,6 +79,7 @@
 ;;; Code:
 
 (eval-when-compile (require 'cl))			      ; to use `push', `pop'
+(require 'format-spec)
 
 (defface git-blame-prefix-face
   '((((background dark)) (:foreground "gray"