Getting rid of `set_status()` calls.
Move `set_status()` private.

This forces the use of the new status codes when creating
`tile_protocol` objects.
No more use of cmd/status in tests.
Convert tile submitting tool.
Converted image handling.
Removed unused, unbuilt source.
Converted worker.
Use the new simpler is_response_okay in response impl
Merge remote-tracking branch 'origin/500_cacheable' into refactor_command_status
Remove public `status()` method on `tile_protocol`.

Also, make the `protoCmd` enum private to the `tile_protocol`
implementation to ensure that none of the rest of the code can
still be using it.
Improvements to documentation.
Fix bug in composite storage.
Merge pull request #23 from MapQuest/refactor_command_status

Refactor command status (part 2)