examples: fix compiler warning about unused variable

Signed-off-by: Sébastien Boisvert <boisvert@anl.gov>
transport: use red-black tree instead of binary heap

The current implementation of the binary heap uses an array.
Inserting into the heap can be O(n) when the array is full and
needs to be resized.

Until the binary heap is implemented with pointers, the multiplexer
is going to rely on the red-black tree.

Signed-off-by: Sébastien Boisvert <boisvert@anl.gov>
scheduler: use red-black tree for scheduling actors

Signed-off-by: Sébastien Boisvert <boisvert@anl.gov>