CCfits 2.4: new formula

This formula is for [`CCfits` 2.4](http://heasarc.gsfc.nasa.gov/fitsio/CCfits/), patched for OS X Mavericks as described in the [official documentation](http://heasarc.gsfc.nasa.gov/fitsio/CCfits/html/).
Does the patch only apply to Mavericks and not earlier versions?