Replace json-c with internal parser

[arun@xxxxxxxxxxxx (arun@xxxxxxxxxxxx)]

Following up with the previous discussion on list about this, and
related to bug #95135, I've implemented our own JSON parsing to allow us
to drop json-c as a dependency.

I've added some tests that I think cover most of the cases we need to be
checking for, but if anyone wants to, please feel free to add some more.

Cheers,
Arun