send-email: enable SSL level 1 debug output

If a server's certificate isn't accepted by send-email, the output is:

	Unable to initialize SMTP properly. Check config and use --smtp-debug.

but adding --smtp-debug=1 just produces the same output since we don't
get as far as talking SMTP.

Turning on SSL debug at level 1 gives:

	DEBUG: .../IO/Socket/SSL.pm:1796: SSL connect attempt failed error:14090086:SSL routines:ssl3_get_server_certificate:certificate verify failed
	DEBUG: .../IO/Socket/SSL.pm:673: fatal SSL error: SSL connect attempt failed error:14090086:SSL routines:ssl3_get_server_certificate:certificate verify failed
	DEBUG: .../IO/Socket/SSL.pm:1780: IO::Socket::IP configuration failed

IO::Socket::SSL defines level 1 debug as "print out errors from
IO::Socket::SSL and ciphers from Net::SSLeay".  In fact, it aliases
Net::SSLeay::trace which is defined to guarantee silence at level 0 and
only emit error messages at level 1, so let's enable it by default.

The modification of warnings is needed to avoid a warning about:

	Name "IO::Socket::SSL::DEBUG" used only once: possible typo

Signed-off-by: John Keeping <john@keeping.me.uk>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

git-send-email.perl

@@ -1318,6 +1318,13 @@ sub send_message {
 			require Net::SMTP::SSL;
 			$smtp_domain ||= maildomain();
 			require IO::Socket::SSL;
+
+			# Suppress "variable accessed once" warning.
+			{
+				no warnings 'once';
+				$IO::Socket::SSL::DEBUG = 1;
+			}
+
 			# Net::SMTP::SSL->new() does not forward any SSL options
 			IO::Socket::SSL::set_client_defaults(
 				ssl_verify_params());