[fitswcs] RADECSYS keyword values

[Mark Calabretta]

The issue of additional RADECSYS keyword values has come to the fore lately.
It seems reasonable to me to support any formally recognized system, hence

   ICRF		...International Celestial Reference Frame
   HIPPARCOS	...Hipparcos

are obvious.  What about "RORF" (Radio-Optical Reference Frame, see for
example http://maia.usno.navy.mil/rorf/)?  Anything else?

This forum should make a decision and respond to Greg Hennessy's post to
fitsbits.

Cheers, Mark