MFC: r283008

MFC: r283008
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.

git-svn-id: svn://svn.freebsd.org/base/stable/10@283762 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f