Add sanity checking for QUEUE(3) lists under INVARIANTS.  Races may lead to list corruption, which can be difficult to unravel in a post-mortem analysis.  These checks verify that prev and next pointers are consistent when inserting or removing elements, thus catching any corruption earlier.
Add sanity checking for QUEUE(3) lists under INVARIANTS.  Races may lead
to list corruption, which can be difficult to unravel in a post-mortem
analysis.  These checks verify that prev and next pointers are consistent
when inserting or removing elements, thus catching any corruption earlier.

Also use TRASHIT to break LIST and SLIST link pointers on element removal,
from mlaier via -hackers.

Reviewed by:	mlaier
Approved by:	rwatson (mentor)

jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase