Following a report of user confusion on the mailing list, let’s switch
up 3b.3 so that instead of saying “do the same as step 3a.3 but...” it
instead copies in the instructions of 3a.3 and adjusts them to match.
The old "libXm" bundled in the XEphem repository isn't compatible with
the underlying libraries in modern Linux, so let's switch to using the
Motif provided by their distribution.