Add a regression test for 'git remote add <existing> <same-url>'

Signed-off-by: NJohannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

t/t5505-remote.sh

@@ -1113,4 +1113,9 @@ test_extra_arg set-url origin newurl oldurl
 # prune takes any number of args
 # update takes any number of args
 
+test_expect_success 'add remote matching the "insteadOf" URL' '
+	git config url.xyz@example.com.insteadOf backup &&
+	git remote add backup xyz@example.com
+'
+
 test_done