Fixed test failure involving doc validation
Fixed behavior of doc purging

The new ForestDB-based implementation wasn't compatible with version 1.0
or CouchDB. Brought its behavior back in line.
Fixed skip/limit options to getAllDocs
Fixed a subtlety of doc insertion

allowConflict=YES in -putRevision: allows a duplicate revision to be
created but only if the _rev property was given; it doesn't apply if
creating a new document. (Caught by the functional test suite.)
Fixed bug in handling of limit and skip in getAllDocs