AUTH PLAIN bug with qpsmtpd and alpine [SOLUTION]

[Rick]

Trying to get SMTP auth working with alpine, I came across a bug.  
Alpine sends AUTH PLAIN and waits for a 334 response, then sends the 
auth string.  According to the RFC, the server should reply with 334 and 
a nothing else, but in Auth.pm qpsmtpd responds with "334 Please 
continue."   the "Please continue" is interpreted as a non-zero length 
initial challenge which causes alpine (and maybe other clients?) to 
abort the session.

The simple fix is to change this part in Auth.pm:
   if ( $mechanism eq "plain" ) {
       if (!$prekey) {
         $session->respond( 334, "Please continue" );
         $prekey= <STDIN>;
       }

To this:

   if ( $mechanism eq "plain" ) {
       if (!$prekey) {
         $session->respond( 334, " " );
         $prekey= <STDIN>;
       }


There's a space in there, otherwise qpsmtpd won't send any response 
which is equally as bad.

I suggest somebody commit this small change to the source tree.
-Rick