Fixes identified by flake8:

Selectors.py:12:1: F401 'operator' imported but unused
FunctionSlot.py:15:1: F401 'inspect' imported but unused
GenomeBase.py:388:7: F841 local variable 'parent' is assigned to but never used
GPopulation.py:242:7: F841 local variable 'fit_sum' is assigned to but never used