BLD: fix path handling, and possible import surprises in test_perf
TST: add test for mom._flex_binary_moment blowing the stack GH3155
BUG: _flex_binary_moment should validate it's arguments' type
TST: added rolling_corr test with cener=True GH3155

Conflicts:
	pandas/stats/tests/test_moments.py
BUG: rolling_corr should pass center=True to it's delegates
DOC: update RELEASE.rst
BUG: fixed issues where passing an axis of 'index' would fail (as its expecting an axis number)