I have made the following changes to support the IRAF ZPX coordinate system.
ZPX is better than the earlier TNX system already supported by ds9.
Support for ZPX is desired because NOAO has a very large archive (tens of
thousands of exposures) of calibrated data from their MOSAIC cameras using
this coordinate system.  In the process of implementing this, a couple of
hacks were included to deal with a) some WAT keywords accidentally placed
in the primary header under the assumption of using the inheritance
convention not supported by this code and b) using a default size if
DETSEC is missing and the user is loading all extensions from an MEF.
For the first problem, the NOAO pipeline has been fixed to not let any
WCS keywords end up in the primary/shared header but the earlier holdings
in the archive will not be changed.

wcssubs-3.7.6/zpxpos.c +
wcssubs-3.7.6/wcs.h
wcssubs-3.7.6/wcs.c
wcssubs-3.7.6/wcsinit.c
wcssubs-3.7.6/worldpos.c
wcssubs-3.7.6/Makefile
wcssubs-3.7.6/Files
     Add driver for IRAF ZPX coordinate system.

wcssubs-3.7.6/hget.c
     If the pre-indexed header search fails use the regular string search.
     This is done to allow adding some missing keywords (actually
     accidentally placed in the primary header using the inheritance
     convention which is not supported in this code) for NOAO MOSAIC
     ZPX data in zpxpos.  There may be a way to reindex a header string but
     the code where this happens was difficult to decipher.

saotk/frame/fitsimage.C
    Instead of failing if DETSIZE is missing use a default size of 10Kx10K.
    This is only needed with the "Open IRAF Mosaic..." option.