Clean out cruft from the master<->worker protocol and add "specify_directory" function.

Eliminated "mkdir", "stat", "symlink", and "get" as redundant, unnecessary or nonsensical in the new system.
Renamed "rget" to "get", so file transfer messages can be put/get instead of put/rget.  Added argument to differentiate between recursive and non-recursive.
Rewrote thirdput/thirdget to work with the new cache/task directory structures.
Collapsed "worker_status", "queue_status" and "task_status" into a single "status" command with an option for {worker|queue|task}.
Removed <fileid> from "put" commands as it is no longer necessary with the way tasks are now described.
Added work_queue_task_specify_directory() for adding empty directories to the task specification.  "dir" is now a sub-command of a task description for requiring an empty directory.

This addresses issues #46 and #90.  All of the tests except for the parrot_search test successfully complete, but I'll wait to close those issues until I can double check and make sure everything works without issue.
Merge branch 'master' of github.com:cooperative-computing-lab/cctools

Conflicts:
	dttools/src/work_queue_status.c