Unite CacheFetchProcs and add abstraction calls.

Unite CacheFetchProcs and add abstraction calls.

The cache type specific differencies among afs_MemCacheFetchProc
and afs_UFSCacheFetchProc are divided into two sets of "fetchOps".
Upon rxfs_fetchInit, the appropriate set is chosen.

Reviewed-on: http://gerrit.openafs.org/109
Tested-by: Derrick Brashear <shadow@dementia.org>
Reviewed-by: Derrick Brashear <shadow@dementia.org>