Extended the JSON_INIT_CLEAR macro to avoid segfaults.

Extended the JSON_INIT_CLEAR macro to avoid segfaults.

Scenario: converting a JSON_BOOL, with a value of true, to a JSON_HASH or
JSON_ARRAY.  The true value (in a union with an osrfHash* and an osrfList*)
was being interpreted as a non_NULL pointer and deferenced.  Oops.

With this change, we clear the boolean value (by nullifying one of the
unioned pointers) whenever changing from a JSON_BOOL to anything else.

git-svn-id: svn://svn.open-ils.org/OpenSRF/trunk@1733 9efc2488-bf62-4759-914b-345cdb29e865