* src/threads/thread.cpp: Use a finalizer to remove dead threads.

* src/threads/thread.cpp: Use a finalizer to remove dead threads.
* src/threads/posix/thread-posix.cpp (threads_impl_clear_heap_pointers): Added.
* src/threads/thread.hpp: Likewise.
* src/threads/posix/thread-posix.hpp: Added flag is_in_active_list.
* src/threads/threadlist.cpp, src/threads/threadlist.hpp: Take thread list lock
for all thread list operations.
(deactivate_thread): Added.
* src/threads/thread-classpath.cpp: Adapted to lock change.