Use IAU 2006 matrix for converting to true coordinates.
Use IAU 2006 matrix for converting to true coordinates.

This is a private function, used only for tests inside astropy,
but also used at times outside of astropy.  As noted by @mkbrewer,
it should be consistent with what is used elsewhere, in particular
in coordinates.builtin_frames.utils.get_cip.

mhvk/astropy,dhomeier/astropy,astropy/astropy,larrybradley/astropy,saimn/astropy,aleksandr-bakanov/astropy,lpsinger/astropy,StuartLittlefair/astropy,saimn/astropy,larrybradley/astropy,astropy/astropy,mhvk/astropy,larrybradley/astropy,mhvk/astropy,larrybradley/astropy,dhomeier/astropy,astropy/astropy,StuartLittlefair/astropy,pllim/astropy,pllim/astropy,mhvk/astropy,astropy/astropy,saimn/astropy,aleksandr-bakanov/astropy,astropy/astropy,dhomeier/astropy,dhomeier/astropy,saimn/astropy,StuartLittlefair/astropy,aleksandr-bakanov/astropy,lpsinger/astropy,pllim/astropy,pllim/astropy,larrybradley/astropy,lpsinger/astropy,lpsinger/astropy,aleksandr-bakanov/astropy,saimn/astropy,StuartLittlefair/astropy,dhomeier/astropy,pllim/astropy,mhvk/astropy,lpsinger/astropy,StuartLittlefair/astropy