Handle null fields.

* Switch the json parser to return a proper null, instead of the special NULL object.
* Compare against null directly
Allow deserialize to parse BytesWritable, which adds support for json embedded in sequence files
Merge commit '1a98eaf2e3a11c82b653bffcb17273f827c11b66'

Conflicts:
	src/main/java/org/openx/data/jsonserde/json/JSONObject.java
Merge commit '044eb2f466ce740f4c4da38fab19787c5dfc9df4'