session directory cleanup (among other things)
- When we get an abnormal exit in orterun (i.e., timeout expires and
we haven't gotten termination notices from all processes), print a
better message an exit in a better way (which includes session
directory cleanup)
- Fix tm and poe pls's to not exit() but rather propagate the error up
the stack (where relevant)
This commit was SVN r7058.
