Added more debugging aids, assertions. Corrected errors, including hangs, at the cost or making the read-write mutex even larger. The whole read-write mutex is too complicated; the design needs to be revisited.

[SVN r27874]

libs/thread

@@ -1 +1 @@
-Subproject commit b9dbb1ed45ae8d52e5dc1944bafcd1c8f5b285e6
+Subproject commit 3b237267fb42ea2f7a96c6eaaca64eee849bbce2