Workers pruned prematurely

[mjrusso]

I didn't see this one before because the behavior changes depending on the pid(s) of the process(es).

• http://github.com/mjrusso/pyres/commit/6390ac7ae199d49a7bba593b24c2c45a83c3f400
• http://github.com/mjrusso/pyres/commit/dfdbe2ff217d915cdf78c2ba5f007408e4ce73bf

[binarymatt]

this has been merged in and pushed up to master