Improve error reporting and improve docs as suggested by Andy, and
adjust `conv` -> `conv*` to fit a naming convention.
original commit: b34817aea5d3c4862e7bb313ee9f5281472a832f
Changed the base language foregin and fcallable forms to accept a list of
conventions, which are each symbols, instead of a single convention, which was
a list of conventions, mostly to make it clear in the grammar what is going on.
base-lang.ss, cp0.ss cpcheck.ss, cpcommonize.ss, cpletrec.ss, cpnanopass.ss,
cprep.ss, cpvalid.ss, interpret.ss, syntax.ss,
Fixed a place where we were checking for eq? of two conventions, which now
should be equal? since it is a list (assuming this list will always be in a
consistent order).
cpcommonize.ss
Removed a spurious definition of convention?
np-languages.ss
original commit: dabf5a8abeaef12cdfcb36d9aac236dda9ac9158
