[cctbxbb] new parallel_map implementation

[Gabor Bunkoczi]

Hi,

I have switched over libtbx.easy_mp.parallel_map to use new code that is 
not susceptible to deadlock when large amounts of data are returned from 
a worker process. This also means that parameters added to parallel_map 
to prevent exactly this are no longer necessary (but will be respected), 
although unlikely to influence performance so much to warrant changing 
existing code.

I have run all tests, but unsure how well this gets tested by regression 
test, so please let me know if you come across something that is amiss.

BW, Gabor