Added try_* varieties of all functions that can block in Thread.Fifo

and Thread.Queue. Added functions to make Thread.Fifo and Thread.Queue
implement the same interface. Let write and try_write return the
number of elements in the fifo/queue. Added fallbacks for Thread.Fifo
and Thread.Queue in nonthreaded mode since it's now possible to use
them in a meaningful way then.

Rev: lib/modules/Thread.pmod:1.37