Now, when no children are available to pass a request to, the parent

Now, when no children are available to pass a request to, the parent
process blocks on a select() call until any child is available.

previously, the parent would sleep 50ms, do a select() poll, sleep again, etc.

The new approach has the potential to be up to almost 50ms faster at finding
an available child when the parent is forced to wait.  plus, polling is just dumb

git-svn-id: svn://svn.open-ils.org/OpenSRF/trunk@785 9efc2488-bf62-4759-914b-345cdb29e865