Minor build cleanups

The configure script was getting confused if run outside of
Starlink without using --without-starlink. This was because
$STARLINK is set in the script if it is not set and the
configure script was assuming $STARLINK would be unset
outside of a Starlink environment. The configure script
now keys off $STARLINK_DIR but that may interact badly
if STARLINK_DIR is set and --without-starlink is used.

An experimental SConstruct build script is now available
for users of scons.

SUN/267 has been synced up with the associated source files.

palIntin now respects the isblank configure check (as it
should have done all along).

Minor clean ups of some source prologues.