Merge first of two changes to add CSetCause support to gas to the CheriBSD
tree:

commit bb1f65d60ec3dc59527c8086b2d19d122f9669b3
Author: Michael Roe <mroe@cornstalk.org.uk>
Date:   Mon Nov 25 15:33:54 2013 +0000

    Added assembler support for the CSetCause opcode.
Merge second of two changes to add CSetCause support to gas to the CheriBSD
tree:

commit ffecec8084ccb5872e4d2e5c5adf8b7af95211ab
Author: Michael Roe <mroe@cornstalk.org.uk>
Date:   Fri Dec 6 16:23:04 2013 +0000

    Changed the opcode encoding of csetcause.