format-patch: Add "--no-stat" as a synonym for "-p"

"-p" means "generate patch" in 'git log' and 'git diff', so it's
quite surprising that it means "suppress diffstat" in
'git format-patch'.

Keep the "-p" option for backward compatibility, but add
"--no-stat" as a more intuitive synonym. For backward compatibility
with scripts, we must allow combinations of --stat and --no-stat.
Signed-off-by: NBjörn Gustavsson <bgustavsson@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

Documentation/diff-options.txt

@@ -14,6 +14,7 @@ endif::git-format-patch[]
 
 ifdef::git-format-patch[]
 -p::
+--no-stat::
 	Generate plain patches without any diffstats.
 endif::git-format-patch[]
 

builtin-log.c

@@ -923,8 +923,9 @@ int cmd_format_patch(int argc, const char **argv, const char *prefix)
 			    "don't output binary diffs"),
 		OPT_BOOLEAN(0, "ignore-if-in-upstream", &ignore_if_in_upstream,
 			    "don't include a patch matching a commit upstream"),
-		OPT_BOOLEAN('p', NULL, &use_patch_format,
-			"show patch format instead of default (patch + stat)"),
+		{ OPTION_BOOLEAN, 'p', "no-stat", &use_patch_format, NULL,
+		  "show patch format instead of default (patch + stat)",
+		  PARSE_OPT_NONEG | PARSE_OPT_NOARG },
 		OPT_GROUP("Messaging"),
 		{ OPTION_CALLBACK, 0, "add-header", NULL, "header",
 			    "add email header", PARSE_OPT_NONEG,