kernel - Add kqueue and fix chflags handling for tmpfs
* Implement kqueue ops for tmpfs so things like tail -f work properly.
* Redo all the chflags handling and checks to use the helper functions,
also getting ridding of the horribly broken FREAD/FWRITE tests on
node->tn_flags (which is the chflags flags, not the open flags).
This fixes chflags handling for tmpfs. Previously doing something
like 'make installkernel ... DESTDIR=<sometmpfs_target>' would fail
on re-install due to chflags not working properly.
* Fix a lost node unlock in tmpfs_chflags()
Reported-by: Nuno Antunes <nuno.antunes@gmail.com>