BUG: Fix for cython version checking closes #9827
closes #9827

Added a cython version check at the top of setup.py; minimum version of 0.19.1. If the minimum isn't met, _CYTHON_INSTALLED sets to false, so the installation can proceed if cython is not needed, but will fail if cython is needed (with an appropriate error message).

Two new travis jobs added to test install_conda and install_pydata flows for the old cython revision, and ensure that pandas setup fails with appropriate error messages. See https://travis-ci.org/ajamian/pandas/builds/58315862 for regression.

merged via https://github.com/pydata/pandas/commit/a134759c681c5d1d92b782dbc7bbc4c3dacaa081

thanks!
 @jreback Is it needed to have that many extra travis envs in the build matrix? Won't that slow down the travis checking of PRs?
 @jorisvandenbossche only 2 extra and they are really quick. (and in the allowed fails anyhow)
 in the .yml you have to duplicate things if you want them to allowed to fail (e.g. once in the definitions and once in the allowed fails section),
 @jreback Ah, OK, that last info was what I didn't know :-) otherwise it looked like a lot extra in the non-allowed to fails
