fixes issue 578 + redblack sentinel NIL node needs to be per-tree and not global   as parent field must be modified during deletion + tested by running 3 ui_tests where I've seen this assert 10x each + this could explain several heap region identification bugs as well
fixes issue 578
+ redblack sentinel NIL node needs to be per-tree and not global
  as parent field must be modified during deletion
+ tested by running 3 ui_tests where I've seen this assert 10x each
+ this could explain several heap region identification bugs as well

git-svn-id: fe3cd4388a6e5a968b09397a3d721fe124e8117a@604 5b54908e-ead4-fc18-b48a-0285e6dbc711

rnk/drmemory,rnk/drmemory,rnk/drmemory,rnk/drmemory