fix worker pool actor scheduling

test synchronize failed in 2014-07-14-22:00:54.

This patch fixes two bugs:

1. The initial placement for an actor must use thread-safe
functions;
2. There are two code paths to schedule an actor on a worker
(actor scheduling queues). One of the path was not correctly
written. This is fixed now.

Link: https://github.com/GeneAssembly/biosal/issues/407
Signed-off-by: Sébastien Boisvert <boisvert@anl.gov>