use broadcast() instead of signal() when signaling the condition-variable Thread...

use broadcast() instead of signal() when signaling the condition-variable Thread::RequestExitAndWait() is waiting for

we could have several thread waiting on the condition and they all need to wake-up.
also added a debug "mTid" field in the class, which contains the tid of the thread (as opposed to pthread_t), this
is useful when debugging under gdb for instance.