Add a warning message to mountd for exported file
systems that are automounted, since that configuration
isn't supported. This still allows the export, since
two emails I received felt that this should not be
disabled. It sends the message to syslog(LOG_ERR..), so that
it goes to the same places as the other messages related
to /etc/exports problems, even though it is a warning and not an error.

Reviewed by: trasz
MFC after: 2 weeks