Tweaks to oils_cstore.c:

Tweaks to oils_cstore.c:

1. Added a couple of const qualifiers.

2. In verifyObjectPCRUD: renamed meta to method_metadata, for clarity.
In many places we use "meta" for class metadata.

3. In verifyObjectPCRUD: when looking for the root of the org tree,
build the where clause object directly instead of incurring the overhead
of jsonParseString().

4. A few lines further down: free the where clause object in only
a single place.

5. In single_hash(): represent a NULL value as a JSON_NULL.

git-svn-id: svn://svn.open-ils.org/ILS/trunk@13583 dcc99617-32d9-48b4-a31d-7c20da2025e4