unit test to repro https://github.com/couchbase/couchbase-lite-android/issues/80
enhance unit test for https://github.com/couchbase/couchbase-lite-android/issues/80
enhance unit test for https://github.com/couchbase/couchbase-lite-android/issues/80
Fix for https://github.com/couchbase/couchbase-lite-android/issues/80.  There is some confusion over content_type vs content-type, and it currently uses both which needs to be fixed in a future commit.
Update for fix for https://github.com/couchbase/couchbase-lite-android/issues/80.  Uses content_type when appropriate, rather than duplicating content-type and content_type
While testing https://github.com/couchbase/couchbase-lite-android/issues/80 found issue where it was not returning the Content-Type header when it should be.  Fixed a clearcut bug in CBLBody#isValidJson to fix this.