Pylint emplike formula genmod

Another small round of fixed for https://github.com/statsmodels/statsmodels/issues/613

At this point, pyflakes is showing no errors in emplike and formula other than import issues in */apy.py.

We can make these go away by either asserting the imports or by silencing pylint (but not pyflakes)

Ref: http://stackoverflow.com/questions/14233867/pylint-ignore-specific-names