Add documentation around zero-length timeouts

Add documentation to cover the fact that wait()
and join() treat zero-length timeouts as "wait indefinitely".
Improved documentation for when a thread is already
interrupted when the various sleep/join/wait calls are made,
and what happens to the interrupted state.

Bug: 12931322
Change-Id: I4e8353cb556ff335df187fd5efa1f42c9b196cd6
4 files changed