This commit should restore the pre-non-blocking behavior of the CID
allocator when threads are used. There are two primary changes: 1)
do not hold the cid allocator lock past the end of a request callback,
and 2) if a lower id communicator is detected during CID allocation
back off and let the lower id communicator finish before continuing.
Signed-off-by: Nathan Hjelm <hjelmn@lanl.gov>
fbbf743c36