Add stop clause for couch_btree
Add stop clause for couch_btree

This is part of "Implement couch_view:get_map_keys/4", the rest was in
couch_view:get_map_keys, a module which no longer exists.

fkaempfer/couchdb,KlausTrainer/couchdb-couch,alanning/couchdb-couch,smithsz/couchdb-couch,fkaempfer/couchdb,alanning/couchdb-couch,ngpestelos/couchdb-couch,ngpestelos/couchdb-couch,KlausTrainer/couchdb-couch,smithsz/couchdb-couch,fkaempfer/couchdb,smithsz/couchdb-couch,apache/couchdb-couch,cloudant/couchdb-couch,KlausTrainer/couchdb-couch,fkaempfer/couchdb,ngpestelos/couchdb-couch,fkaempfer/couchdb,cloudant/couchdb-couch,apache/couchdb-couch,cloudant/couchdb-couch,alanning/couchdb-couch,apache/couchdb-couch,fkaempfer/couchdb