timeout_barrier(9), timeout_del_barrier(9): remove kernel lock

timeout_barrier(9), timeout_del_barrier(9): remove kernel lock

In timeout_barrier(9) we take/release the kernel lock to ensure that the
given timeout has finished running (if it had been running at all).

This approach is inefficient.  If we put a barrier timeout on the
queue and wait for it to run in cond_wait(9) we can block instead of
spinning for the kernel lock.  We already do this for process-context
timeouts in timeout_barrier(9) anyway.

Discussed with dlg@, visa@, and mpi@.

ok dlg@