send-email: Handle "GIT:" rather than "GIT: " during --compose

This should make things a little more robust in terms of user input;
before, even the program got it wrong by outputting a line with only
"GIT:", which was left in place as a header, because there would be
no following space character.

Signed-off-by: Michael Witten <mfwitten@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

git-send-email.perl

@@ -529,7 +529,7 @@ ($)
 
 	print C <<EOT;
 From $tpl_sender # This line is ignored.
-GIT: Lines beginning in "GIT: " will be removed.
+GIT: Lines beginning in "GIT:" will be removed.
 GIT: Consider including an overall diffstat or table of contents
 GIT: for the patch you are writing.
 GIT:
@@ -562,7 +562,7 @@ ($)
 	my $in_body = 0;
 	my $summary_empty = 1;
 	while(<C>) {
-		next if m/^GIT: /;
+		next if m/^GIT:/;
 		if ($in_body) {
 			$summary_empty = 0 unless (/^\n$/);
 		} elsif (/^\n$/) {