- added rq_type field to ptlrpc_request

- added rq_type field to ptlrpc_request
- this field must be one of PTLRPC_REQUEST, PTLRPC_REPLY, PTLRPC_BULK
- mdc_request now waits for directory pages to be sent via the bulk portal
- change MDS bulk waitq to the new style
- ptl_send_buf no longer takes the 'is_request' argument; this is encoded in
  the rq_type mentioned above
- added ptl_abort_rpc() to tear down reply structures for aborted requests.
- refactored ptl_send_buf code to rid ourselves of some of the more gross
  bulklen hacks