mount - Split mount into mount_ufs, auto-detect fstype from disklabel

mount - Split mount into mount_ufs, auto-detect fstype from disklabel

* Move the compiled-in ufs mount code from mount to a new utility called
  mount_ufs.

* When mount determines the filesystem type is ufs it now exec's mount_ufs
  instead of calling the built-in ufs code.

* When mounting a disklabeled device and the fstype is not specified
  mount will attempt to figure out the fstype from the disklabel.

  Devices matching acd%d and cd%d will default to the 'cd9660' fstype.

  It defaults to ufs if it cannot figure it out (as before).

* If your filesystems are properly labeled this allows you to specify
  the mount generically as in this example:

      mount /dev/da0s1d /mnt

  And mount will exec mount_ufs or mount_hammer (etc...) as appropriate.

* NOTE! mount cannot currently auto-detect msdosfs or extract the DOS
  slice type.  It would be cool if it were extended further to do this
  as well.  Currently it only understands DragonFly disklabels.