Unite CacheStoreProcs and add abstraction calls.

Unite CacheStoreProcs and add abstraction calls.

The cache type specific differencies among afs_MemCacheStoreProc
and afs_UFSCacheStoreProc are divided into two sets of "storeOps".
Upon rxfs_storeInit, the appropriate set is chosen.

FIXME: Simon suggests that there should be a single set of storeOps,
as the main difference lies in what rx_ calls must be made.
This decision would then be made by calling a wrapper function from
each storeOp. These wrappers should be cachetype-specific and protocol-
independent. They would be associated to struct afs_cacheOps.
Reviewed-on: http://gerrit.openafs.org/http://gerrit.openafs.org/107
Tested-by: Russ Allbery <rra@stanford.edu>
Reviewed-by: Russ Allbery <rra@stanford.edu>