pvfs: add PVFS_RESOLVE_NO_OPENDB flag and get the write time from the opendb

pvfs: add PVFS_RESOLVE_NO_OPENDB flag and get the write time from the opendb

By default get the current write time from the opendb,
but allow callers to pass PVFS_RESOLVE_NO_OPENDB
for performance reasons, if they don't need to the write time.

metze
(This used to be commit def52cc0988c26a815e74b3391e5857512408d90)