Disable mmaps for io (double counting)
Make exit event synchronous.
Execute command directly, rather than using sh

When using sh, the monitor would count one more fork (forking sh, and
then sh forking the task to be monitoring).
Bump to 4.1.0rc2
Added hook to allow makeflow to specify WQ activate worker waiting.
Fixed race condition between simultaneous parrots creating the cache directory.  Check for the case where mkdir fails because the directory already exists.
Use mkdir rather than create_dir for subdirectories, to avoid n^2
traversal of the directory hierarchy.