git-send-email: honor $PATH for sendmail binary

This extends git-send-email to also consider sendmail binaries in $PATH
after checking the (fixed) list of /usr/sbin and /usr/lib, and before
falling back to localhost.

Signed-off-by: Florian Klink <flokli@flokli.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: flokli

Documentation/git-send-email.txt

@@ -203,9 +203,9 @@ a password is obtained using 'git-credential'.
 	specify a full pathname of a sendmail-like program instead;
 	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.
+	option; the built-in default is to search for `sendmail` in
+	`/usr/sbin`, `/usr/lib` and $PATH if such program is
+	available, falling back to `localhost` otherwise.
 
 --smtp-server-port=<port>::
 	Specifies a port different from the default port (SMTP

git-send-email.perl

@@ -885,7 +885,9 @@ sub expand_one_alias {
 }
 
 if (!defined $smtp_server) {
-	foreach (qw( /usr/sbin/sendmail /usr/lib/sendmail )) {
+	my @sendmail_paths = qw( /usr/sbin/sendmail /usr/lib/sendmail );
+	push @sendmail_paths, map {"$_/sendmail"} split /:/, $ENV{PATH};
+	foreach (@sendmail_paths) {
 		if (-x $_) {
 			$smtp_server = $_;
 			last;