diff: accept --no-follow option

Once you do

	$ alias glogone git log --follow

there is no way to say

	$ glogone --no-follow ...

Not that "log --follow" is all that useful, but it is cheap to
support the common "you can defeat an undesirable option with a
'no-' variant of it later on the command line" pattern.

Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff.c

@@ -3584,6 +3584,8 @@ int diff_opt_parse(struct diff_options *options, const char **av, int ac)
 		DIFF_OPT_SET(options, FIND_COPIES_HARDER);
 	else if (!strcmp(arg, "--follow"))
 		DIFF_OPT_SET(options, FOLLOW_RENAMES);
+	else if (!strcmp(arg, "--no-follow"))
+		DIFF_OPT_CLR(options, FOLLOW_RENAMES);
 	else if (!strcmp(arg, "--color"))
 		options->use_color = 1;
 	else if (!prefixcmp(arg, "--color=")) {