git-send-email: Read the default SMTP server from the GIT config file

Make the default value for --smtp-server configurable through the
'sendemail.smtpserver' option in .git/config (or $HOME/.gitconfig).

Signed-off-by: Sergey Vlasov <vsu@altlinux.ru>
Acked-by: Ryan Anderson <rda@google.com>
Signed-off-by: Junio C Hamano <junkio@cox.net>

Documentation/git-send-email.txt

@@ -68,9 +68,11 @@ The options available are:
 --smtp-server::
 	If set, specifies the outgoing SMTP server to use.  A full
 	pathname of a sendmail-like program can be specified instead;
-	the program must support the `-i` option.  Defaults to
-	`/usr/sbin/sendmail` or `/usr/lib/sendmail` if such program is
-	available, or to `localhost` otherwise.
+	the program must support the `-i` option.  Default value can
+	be specified by the 'sendemail.smtpserver' configuration
+	option; the built-in default is `/usr/sbin/sendmail` or
+	`/usr/lib/sendmail` if such program is available, or
+	`localhost` otherwise.
 
 --subject::
    	Specify the initial subject of the email thread.

git-send-email.perl

@@ -230,6 +230,9 @@ sub expand_aliases {
 	$initial_reply_to =~ s/(^\s+|\s+$)//g;
 }
 
+if (!$smtp_server) {
+	$smtp_server = $repo->config('sendemail.smtpserver');
+}
 if (!$smtp_server) {
 	foreach (qw( /usr/sbin/sendmail /usr/lib/sendmail )) {
 		if (-x $_) {