Associate #:replace info with modules, not variables

* doc/ref/api-modules.texi (Creating Guile Modules): Document
  #:re-export-and-replace.
* module/ice-9/boot-9.scm (module-replacements): New module field.
  (make-module, make-autoload-interface): Initialize replacements to an
  empty hash table.
  (resolve-interface): Propagate replacement info when making custom
  interfaces.
  (define-module): Parse a #:re-export-and-replace keyword arg.
  (define-module*): Handle #:re-export-and-replace.
  (module-export!, module-re-export!): Add a keyword arg to indicate
  whether to replace or not.
  (module-replace!): Call module-export! with #:replace? #t.
  (duplicate-handlers): Update replace duplicate handler to look for
  replacement info on the interfaces.
* module/srfi/srfi-18.scm (srfi):
* module/srfi/srfi-34.scm (srfi): Update to #:re-export-and-replace
  raise-continuable as raise.

module/srfi/srfi-18.scm

@@ -76,8 +76,8 @@
             terminated-thread-exception?
             uncaught-exception?
             uncaught-exception-reason)
-  #:re-export ((raise-continuable . raise)
-               with-exception-handler)
+  #:re-export (with-exception-handler)
+  #:re-export-and-replace ((raise-continuable . raise))
   #:replace (current-time
              current-thread
              thread?