OSX lock initialization cleanup

OSX lock initialization cleanup

Move GLOCK creation before other things at modload time. Also
remove unused rwlock support from rx kmutex package.

Reviewed-on: http://gerrit.openafs.org/http://gerrit.openafs.org/170
Reviewed-by: Simon Wilkinson <sxw@inf.ed.ac.uk>
Tested-by: Derrick Brashear <shadow@dementia.org>
Reviewed-by: Derrick Brashear <shadow@dementia.org>