diff: properly error out when combining multiple pickaxe options

In f506b8e8b5 (git log/diff: add -G<regexp> that greps in the patch text,
2010-08-23) we were hesitant to check if the user requests both -S and
-G at the same time. Now that the pickaxe family also offers --find-object,
which looks slightly more different than the former two, let's add a check
that those are not used at the same time.

Signed-off-by: Stefan Beller <sbeller@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff.c

@@ -4123,6 +4123,9 @@ void diff_setup_done(struct diff_options *options)
 	if (count > 1)
 		die(_("--name-only, --name-status, --check and -s are mutually exclusive"));
 
+	if (HAS_MULTI_BITS(options->pickaxe_opts & DIFF_PICKAXE_KINDS_MASK))
+		die(_("-G, -S and --find-object are mutually exclusive"));
+
 	/*
 	 * Most of the time we can say "there are changes"
 	 * only by checking if there are changed paths, but

diffcore-pickaxe.c

@@ -251,7 +251,6 @@ void diffcore_pickaxe(struct diff_options *o)
 		}
 	}
 
-	/* Might want to warn when both S and G are on; I don't care... */
 	pickaxe(&diff_queued_diff, o, regexp, kws,
 		(opts & DIFF_PICKAXE_KIND_G) ? diff_grep : has_changes);