FIX: Use json-bigint module to properly handle the too-big-number issue in classic json parsing.

Add the test-cases that show the need for this in regular solr fields of type long (_l suffix)
and the fact that the solr 4.x optimistic locking feature (ie the  _version_ field) needs this badly.

Close #71

Conflicts:

	lib/solr.js
NEW: Update json-bigint to the latest version 0.1.3.