[R6RS] modules

[R. Kent Dybvig]

> Now that I have thought about this a bit more, this is my preference
> as well, with caveat that I would prefer that the declarations of
> "implicit" exports be done automatically for uses of SYNTAX-RULES.

Unfortunately, the problems that arise with possible implicit export
names appearing in syntax objects in more general macros also arise
with syntax-rules.  Thus, the analysis is still complex, potentially
expensive, and conservative.

Kent