(2.7) chimera: fix get locality to work with id-type FsInode

The current implementation of ".(get)(filename)(locality)" relies on an FsInode type which embeds the filename and the "locality" argument.  Since the filename is arbitrarily long, the encoded handle length could exceed the file handle length specified by NFS4.

The solution is to change the handling of this command (file) to use the id FsInode type and to encode the operation directly into it.  The id (pnfsid) is of fixed length, as is the code for the op.

A new FsInode type (PLOC) has been created for this purpose.  Several auxiliary methods and private classes which are no longer necessary have also been eliminated.

The new code allows this operation to work successfully with both v4 and with the smaller handle size of v3 as well (both were tested).

Target: 2.7
Patch: http://rb.dcache.org/r/6404
Require-book: no
Require-notes: yes
Acked-by: Tigran
Committed: 9657929930ea0503462116835ecb98f1cc4587ba

RELEASE NOTES:  Fixes a bug in the ".(get)(filename)(locality)" preventing successful completion of the call when the filename is very long.
Merge pull request #374 from alrossi/fix/2.7/get_locality

(2.7) chimera: fix get locality to work with id-type FsInode