Use a dynamically sized xdr_array to pass memory stats on the wire.  This
supports the addition of future memory stats and reduces the message size
since only supported statistics are returned.

* src/remote/remote_protocol.x: provide defines for the new entry point
* src/remote/remote_driver.c daemon/remote.c: implement the client and
  server side
* daemon/remote_dispatch_args.h daemon/remote_dispatch_prototypes.h
  daemon/remote_dispatch_ret.h daemon/remote_dispatch_table.h
  src/remote/remote_protocol.c src/remote/remote_protocol.h: generated
  stubs