[Users] procmsg.c: Error vs Warning on Send

[Pierre Fortin]

Kept getting an Error while sending large messages...

Shouldn't the following dialog be a Warning?  It's not really an Error
when a message is queued simply because there's already a message being
sent...

   Error
   Already trying to send.
   Use "Send queued messages" from the main window to retry.

Also, the user does not need to use "Send queued messages" in this case
since the queued messages get sent without intervention as the previous
one(s) complete; thus making even a Warning redundant.