Oops, fixed compile errors in unit tests
Use updated fdb iterator API. Don't use iterators for doc-array enumeration.

TEMPORARY: Based on in-review forestdb commit, not yet in master
Don't leak opened fdb_kvs_handles

fdb_kvs_open returns a newly-allocated handle every time it's called
with the same name, so Database now keeps track of opened handles by
name.
Fixed crash enumerating empty db. Added more enumeration test cases.
Updated forestdb (added new source files to project)
Cleaned up and simplified enumerator classes.

Using enumerators works a bit differently now. See the doc-comments for
the DocEnumerator and IndexEnumerator classes.
Update to latest ForestDB iterator API change to fdb_iterator_seek

CBForest unit tests pass now
Use FDB_ITR_SKIP_MAX/MIN_KEY flags for non-inclusive start/end