Threads: Fixed hang in co_wait_interpreter().

co_wait_interpreter() would hang (waiting for threads to be
reenabled) if called in a disabled_thread context. This happens
on OSes using USE_WAIT_THREAD (eg Solaris) if a process is waited
on in a disabled_thread context.
Threads: Fixed hang in co_wait_interpreter_timeout().

Same bug as previously fixed in co_wait_interpreter().