t9001: use existing helper in send-email test

Use the wrapper function around the sed statement like everywhere
else in the test. Unfortunately the wrapper function is defined
pretty late.

Move the wrapper to the top of the test file, so future users have it
available right away.

Signed-off-by: Christian Ludwig <chrissicool@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t9001-send-email.sh

@@ -6,6 +6,12 @@ test_description='git send-email'
 # May be altered later in the test
 PREREQ="PERL"
 
+replace_variable_fields () {
+	sed	-e "s/^\(Date:\).*/\1 DATE-STRING/" \
+		-e "s/^\(Message-Id:\).*/\1 MESSAGE-ID-STRING/" \
+		-e "s/^\(X-Mailer:\).*/\1 X-MAILER-STRING/"
+}
+
 test_expect_success $PREREQ 'prepare reference tree' '
 	echo "1A quick brown fox jumps over the" >file &&
 	echo "lazy dog" >>file &&
@@ -293,10 +299,7 @@ test_expect_success $PREREQ 'Show all headers' '
 		--bcc=bcc@example.com \
 		--in-reply-to="<unique-message-id@example.com>" \
 		--smtp-server relay.example.com \
-		$patches |
-	sed	-e "s/^\(Date:\).*/\1 DATE-STRING/" \
-		-e "s/^\(Message-Id:\).*/\1 MESSAGE-ID-STRING/" \
-		-e "s/^\(X-Mailer:\).*/\1 X-MAILER-STRING/" \
+		$patches | replace_variable_fields \
 		>actual-show-all-headers &&
 	test_cmp expected-show-all-headers actual-show-all-headers
 '
@@ -551,12 +554,6 @@ Result: OK
 EOF
 "
 
-replace_variable_fields () {
-	sed	-e "s/^\(Date:\).*/\1 DATE-STRING/" \
-		-e "s/^\(Message-Id:\).*/\1 MESSAGE-ID-STRING/" \
-		-e "s/^\(X-Mailer:\).*/\1 X-MAILER-STRING/"
-}
-
 test_suppression () {
 	git send-email \
 		--dry-run \