compilation passes return third value: the continuation environment

* 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.

module/language/objcode/spec.scm

@@ -40,8 +40,8 @@
         (save-module-excursion
          (lambda ()
            (set-current-module (objcode-env-module e))
-           (values (thunk) #f)))
-        (values (thunk) #f))))
+           (values (thunk) #f e)))
+        (values (thunk) #f e))))
 
 ;; since locals are allocated on the stack and can have limited scope,
 ;; in many cases we use one local for more than one lexical variable. so