Fix and document naming convention for vnode variables (always use
lvp/lvpp and uvp/uvpp instead of a hash of cvp, vpp, dvpp, pvp, pvpp).
Delete old stale #if 0'ed code at the end.
Change error path code in getcwd_getcache() slightly (merge common
cleanup code; shouldn't affect behavior any).
Add kernel implementation of getcwd() which uses this cache, falling
back to reading the filesystem on a cache miss.
Along for the ride: add new VOP_FSYNC flag FSYNC_RECLAIM indicating
that a reclaim is being done, so only a "shallow" fsync is needed.
