Introduce the concept of previously mounted media to sysinstall. This will now allow sysinstall to work properly if a FreeBSD CD/DVD is already mounted as /cdrom, instead of just crapping out when it tries to mount as /dist and gets EBUSY.
Introduce the concept of previously mounted media to sysinstall.
This will now allow sysinstall to work properly if a FreeBSD CD/DVD is
already mounted as /cdrom, instead of just crapping out when it tries
to mount as /dist and gets EBUSY.

PR:		conf/28081
Tested by:	jhb

jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase