Restore Lookup#each_tuple_space

It is needed by Lookup#find
Fix Lookup#wait_for

Previous implementations of Lookup#wait_for could get stuck doing
nothing and waiting forever or busy-looping and consuming lots of
traffic.

Now #enumerate_tuple_spaces continually yields tuple spaces even if
they've been found before.  #wait_for now cancels the renewer for the
last tuple space and creates a new one for the current batch.