Stack usage is my enemy. Trade cpu cycles in the debug code to
ensure I never add anything to the stack I don't absolutely need.
All this debug code could be removed from a production build
anyway so I'm not so worried about the performance impact. We
may also consider revisting the mutex and condvar implementation
to ensure no additional stack is used there.

Initial indications are I have reduced the worst case stack
usage to 9080 bytes. Still to large for the default 8k stacks
so I have been forced to run with 16k stacks until I can
reduce the worst offenders.

git-svn-id: https://outreach.scidac.gov/svn/spl/trunk@83 7e1ea52c-4ff2-0310-8f11-9dd32ca42a1c