Check that WCS of slice is properly returned if input was data and WCS object.
Updated astropy_helpers to v0.4.2
Avoid running functions in pytest decorator at import time
Merge pull request #52 from astrofrog/fix-wcs-logic

Error in logic of extract_pv_slice for WCS
allow wcs to be passed to polygon factory
Merge pull request #53 from keflavich/wcs_for_poly

allow wcs to be passed to polygon factory