diff-options: make --patch a synonym for -p

Here we simply make --patch a synonym for -p, whose mnemonic was "patch"
all along.
Signed-off-by: NWill Palmer <wmpalmer@gmail.com>
Reviewed-by: NJeff King <peff@peff.net>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

Documentation/diff-options.txt

@@ -21,6 +21,7 @@ endif::git-format-patch[]
 ifndef::git-format-patch[]
 -p::
 -u::
+--patch::
 	Generate patch (see section on generating patches).
 	{git-diff? This is the default.}
 endif::git-format-patch[]

diff.c

@@ -2701,7 +2701,7 @@ int diff_opt_parse(struct diff_options *options, const char **av, int ac)
 	const char *arg = av[0];
 
 	/* Output format options */
-	if (!strcmp(arg, "-p") || !strcmp(arg, "-u"))
+	if (!strcmp(arg, "-p") || !strcmp(arg, "-u") || !strcmp(arg, "--patch"))
 		options->output_format |= DIFF_FORMAT_PATCH;
 	else if (opt_arg(arg, 'U', "unified", &options->context))
 		options->output_format |= DIFF_FORMAT_PATCH;