* module/system/base/compile.scm: Expect compile passes to produce three
values, not two. The third is the "continuation environment", the
environment that can be used to compile a subsequent expression from
the same source language. For example, expansion-time side effects can
set the current module, which would be reflected appropriately in the
continuation environment.
* module/language/assembly/compile-bytecode.scm:
* module/language/bytecode/spec.scm:
* module/language/ecmascript/compile-ghil.scm:
* module/language/ghil/compile-glil.scm:
* module/language/glil/spec.scm:
* module/language/objcode/spec.scm:
* module/language/scheme/compile-ghil.scm:
* module/system/base/compile.scm: Update compile passes to return a
continuation environment.