git-send-email.perl: Fixed sending of many/huge changes/patches

Sometimes sending huge patches/commits fail with

[Net::SMTP::SSL] Connection closed at /usr/lib/git-core/git-send-email
line 1320.

Running the command with --smtp-debug=1 yields to

Net::SMTP::SSL: Net::Cmd::datasend(): unexpected EOF on command channel:
at /usr/lib/git-core/git-send-email line 1320.
[Net::SMTP::SSL] Connection closed at /usr/lib/git-core/git-send-email
line 1320.

Stefan described it in his mail like this:

It seems to me that there is a size limit, after cutting down the patch
to ~16K, sending started to work. I cut it twice, once by removing lines
from the head and once from the bottom, in both cases at the size of
around 16K I could send the patch.

See also original report:
http://permalink.gmane.org/gmane.comp.version-control.git/274569

Reported-by: Juston Li <juston.h.li@gmail.com>
Tested-by: Markos Chandras <hwoarang@gentoo.org>
Signed-off-by: Lars Wendler <polynomial-c@gentoo.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

git-send-email.perl

@@ -1282,7 +1282,11 @@ sub send_message {
 		$smtp->mail( $raw_from ) or die $smtp->message;
 		$smtp->to( @recipients ) or die $smtp->message;
 		$smtp->data or die $smtp->message;
-		$smtp->datasend("$header\n$message") or die $smtp->message;
+		$smtp->datasend("$header\n") or die $smtp->message;
+		my @lines = split /^/, $message;
+		foreach my $line (@lines) {
+			$smtp->datasend("$line") or die $smtp->message;
+		}
 		$smtp->dataend() or die $smtp->message;
 		$smtp->code =~ /250|200/ or die "Failed to send $subject\n".$smtp->message;
 	}