Revert "return empty ancestors list when necessary. this fixes function_clause in _revs_diff calls."
Revert "return empty ancestors list when necessary. this fixes function_clause in _revs_diff calls."

This reverts commit 111abfb1638a9f500af89f00f4508afb942b40a7.

fkaempfer/couchdb,fkaempfer/couchdb,fkaempfer/couchdb,fkaempfer/couchdb,fkaempfer/couchdb,fkaempfer/couchdb