CBLModel's save method shouldn't trigger -didLoadFromDocument call

CBLModel saw an echo of its own document change and treated it as an
external change, causing it to reload its properties. This was
wasteful. Fixed it. (Fixes #52)
Speculative fix of a warning from CBLSocketChangeTracker

Fixes the only way I can find to reach the warning "input stream read
returned 0".

See Message-ID 292d3b0e-b304-4306-9d9a-a80da31c0b70@googlegroups.com
CBLModel support for typed array properties (including arrays of models)

Docs on the wiki at:
https://github.com/couchbase/couchbase-lite-ios/wiki/Guide%3A-Models
Fixes #51.
Two small fixes suggested by the Clang static analyzer