simplify ufs cache mechanisms available

simplify ufs cache mechanisms available

instead of having use_fh for linux, vnode_path for solaris and darwin,
use the same mechanism for both. for darwin/solaris we cache the path
(tested via gop_lookupname) instead of an fh, freeing the path at
shutdown.

Change-Id: Id22052db0803264bdaba6b870d9e511953e348bc
Reviewed-on: http://gerrit.openafs.org/1132
Tested-by: Derrick Brashear <shadow@dementia.org>
Reviewed-by: Derrick Brashear <shadow@dementia.org>