Add support for methods to the OSD subsystem. Each object type has a

Add support for methods to the OSD subsystem.  Each object type has a
predefined set of methods, which are set in osd_register() and called
via osd_call().  Currently, no methods are defined, though prison
objects will have some in the future.

Expand the locking from a single per-type mutex to three different kinds
of locks (four if you include the requirement that the container
(e.g. prison) be locked when getting/setting data).  This clears up one
existing issue, as well as others added by the method support.

Approved by:	bz (mentor)