i18n: send-email: mark composing message for translation

When composing an e-mail, there is a message for the user whose lines
begin in "GIT:" that can be marked for translation.

Signed-off-by: Vasco Almeida <vascomalmeida@sapo.pt>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

git-send-email.perl

@@ -672,18 +672,20 @@ sub get_patch_subject {
 	my $tpl_subject = $initial_subject || '';
 	my $tpl_reply_to = $initial_reply_to || '';
 
-	print $c <<EOT;
+	print $c <<EOT1, Git::prefix_lines("GIT: ", __ <<EOT2), <<EOT3;
 From $tpl_sender # This line is ignored.
-GIT: Lines beginning in "GIT:" will be removed.
-GIT: Consider including an overall diffstat or table of contents
-GIT: for the patch you are writing.
-GIT:
-GIT: Clear the body content if you don't wish to send a summary.
+EOT1
+Lines beginning in "GIT:" will be removed.
+Consider including an overall diffstat or table of contents
+for the patch you are writing.
+
+Clear the body content if you don't wish to send a summary.
+EOT2
 From: $tpl_sender
 Subject: $tpl_subject
 In-Reply-To: $tpl_reply_to
 
-EOT
+EOT3
 	for my $f (@files) {
 		print $c get_patch_subject($f);
 	}