pmCoordTPToSky and pmCoordSkyToTP not well defined

[eugene]

these functions are not clearly described. they are also probably wrong. they
should take a pmFPA as the input rather than a psProjection. there should be
two modes; in the simple mode, the pmFPA.projection is just passed to psProject
/ psDeproject. In the complex mode, the EOC Alt/Az -> RA/DEC code should be
used, based on the header information. the celestial projection is a
representation of the full Alt/Az <-> RA/DEC conversion.

[Paul Price]

This probably won't work as we originally envisioned.