Bug 1042929 - Don't throw Errors from JSONObject parsing problems.

org.json.simple and Yylex are badly written: rather than correctly
handling parse errors, the JSON parser allows Yylex's Errors to
propagate to callers, which ordinary Exception handlers won't catch.

This patch rewrites those Errors as ParseExceptions, which will avoid
errors in all consumers.
Bug 1042929 - Don't throw Errors from JSONObject parsing problems. r=mcomella