Updates to support MR8Q312: SDFITS keyword updates.

Rationalization of use of OBSID, SCANID and PROCTYPE
https://safe.nrao.edu/wiki/bin/view/GB/Software/ModificationRequest8Q312

The map finding code uses PROCSCAN when it is present (which it should
be from now on as a default setting).  Otherwise, it uses OBSID as it
did previously.