to have an SEXP_ prefix. Now all values from the headers
are prefixed with either sexp_ or SEXP_, important for ease
of embedding. "make USE_BOEHM=1" still works as an alias
for "make SEXP_USE_BOEHM=1".
Sorry if this patch breaks your code, it had to be done
sooner or later.
and non-mutated identifiers. helps a lot with the default
syntax-rules constructions - in particular reduces the number of
bytecode allocations for (chibi match) from 2397 to 1872.
