PR #140 introduced a feature for the MultiprocessingEvaluator to take a negative input for n_processes, which initialize the evaluator with the cpu_count minus that negative integer, leaving that number of cores free.

In 7dd1610 this code was refactored, introducing a bug that broke the negative-integer input functionality. When a negative integer is inputted, a AttributeError: 'MultiprocessingEvaluator' object has no attribute 'n_processes' was created.

The bug was caused by self.n_processes begin used instead of n_processes, where in earlier code self.n_processes was set equal to n_processes earlier in the process.

Unfortunately this bug landed in the EMAworkbench 2.2.0 release.