Remove dead containers from RC_LIST WARNING MEMORY LEAK

LEAKS MEMORY! need to stgFree the ResourceContainer struct,
but then we need to invalidate existing RC# pointers.  A little
tricky, so don't bother for now.

Tightens up some invariants, yay!

Signed-off-by: Edward Z. Yang <ezyang@mit.edu>
Boogfix

Signed-off-by: Edward Z. Yang <ezyang@mit.edu>
Only conclude it's dead on major_gc

Signed-off-by: Edward Z. Yang <ezyang@mit.edu>
Buggy pinned support

Signed-off-by: Edward Z. Yang <ezyang@mit.edu>