diff: don't run pager if user asked for a diff style exit code

As Wincent Colaiuta found out, it's a bit unexpected for git diff to
start a pager even when the --quiet option is specified.  The problem
is that the pager hides the return code -- which is the only output
we're interested in in this case.

Push pager setup down into builtin-diff.c and don't start the pager
if --exit-code or --quiet (which implies --exit-code) was specified.

Signed-off-by: Rene Scharfe <rene.scharfe@lsrfire.ath.cx>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin-diff.c

@@ -235,6 +235,12 @@ int cmd_diff(int argc, const char **argv, const char *prefix)
 	rev.diffopt.allow_external = 1;
 	rev.diffopt.recursive = 1;
 
+	/* If the user asked for our exit code then don't start a
+	 * pager or we would end up reporting its exit code instead.
+	 */
+	if (!rev.diffopt.exit_with_status)
+		setup_pager();
+
 	/* Do we have --cached and not have a pending object, then
 	 * default to HEAD by hand.  Eek.
 	 */

git.c

@@ -325,7 +325,7 @@ static void handle_internal_command(int argc, const char **argv)
 		{ "config", cmd_config },
 		{ "count-objects", cmd_count_objects, RUN_SETUP },
 		{ "describe", cmd_describe, RUN_SETUP },
-		{ "diff", cmd_diff, USE_PAGER },
+		{ "diff", cmd_diff },
 		{ "diff-files", cmd_diff_files },
 		{ "diff-index", cmd_diff_index, RUN_SETUP },
 		{ "diff-tree", cmd_diff_tree, RUN_SETUP },