Properly trim the vendor tree to include only those files that we want
merged into FreeBSD. Cherry picking from a full vendor tree was too
hard and lead to undestirable svn results.

Note: We only tim the dts* files, we don't trim the dt-bindings tree,
since having all of them causes no problems and the benefit to
trimming there is far out weighed by the cost of doing the trim each
time.
Reimport dts files from vendor repo now that it has been properly
trimmed.
sh: Allow enabling job control without a tty in non-interactive mode.

If no tty is available, 'set -m' is still useful to put jobs in their own
process groups.
Fix a bug which prevented mount.fstab parameter from being converted
when jail_JID_devfs_enable=NO.

Spotted by:	peter