o Make the Makefile respect CC, and respect CFLAGS when linking, too.
o Make a comparison for fputs() success "retval >= 0". Our manual says
fputs() returns 0 on success, but K&R says that it can return any non-
negative int on success. I might as well support either!
o Fix an improper bounds check. It was a simple case of a variable being
mixed up, and this prevents "calc really long arg list (REALLY LONG)"
from crashing calc.
This is just cleaning up the changes I effected earlier with the
maintainer's permission.
