Avoid unnecessarily updating .. in SAFSS_Rename

Avoid unnecessarily updating .. in SAFSS_Rename

Currently the .. entry for a directory is always recreated on a Rename
operation, even if the parent directory does not change. Now, avoid
altering the directory at all (including no COW nor DV bump nor vnode
modify time update) when we don't need to.

Change-Id: I53478ec05e2fc6362836043476ff67e2c41b7feb
Reviewed-on: http://gerrit.openafs.org/436
Reviewed-by: Derrick Brashear <shadow@dementia.org>
Tested-by: Derrick Brashear <shadow@dementia.org>