REF/TST: implement test_interpolate for Series
thanks

btw we should just blow away pandas/tests/generic and put those in series/frame as appropriate (e.g. interpolate tests for frame are there) > btw we should just blow away pandas/tests/generic and put those in series/frame as appropriate (e.g. interpolate tests for frame are there)

This may come as a shock, but I've got a branch that works in that direction. lol