Implement SYSREF - structural reference counting, allocation, and sysid

Implement SYSREF - structural reference counting, allocation, and sysid
management subsystem.

* Structural reference count management, including creation and termination
  sequencing (e.g. where the structure might be temporarily referenced
  during termination).

* Allocation.  It uses an objcache backend for optimal allocation,
  deallocation, and memory recovery.

* Sysid assignment and red-black tree indexing.  It does this in the
  objcache CTOR and DTOR so it costs us absolutely nothing in the
  resource allocation / deallocation critical path.  sysids will be
  reused unless they are externally accessed.