git send-email: interpret unknown files as revision lists

Filter out all the arguments git-send-email doesn't like to a
git format-patch command, that dumps its content to a safe directory.

Barf when a file/revision conflict occurs, allow it to be overriden
--[no-]format-patch.

Signed-off-by: Pierre Habouzit <madcoder@debian.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t9001-send-email.sh

@@ -292,4 +292,12 @@ test_expect_success '--compose adds MIME for utf8 subject' '
 	grep "^Subject: =?utf-8?q?utf8-s=C3=BCbj=C3=ABct?=" msgtxt1
 '
 
+test_expect_success 'detects ambiguous reference/file conflict' '
+	echo master > master &&
+	git add master &&
+	git commit -m"add master" &&
+	test_must_fail git send-email --dry-run master 2>errors &&
+	grep disambiguate errors
+'
+
 test_done