Add json_spirit to build.
Add json_spirit to build.

Add json_spirit by adding it as a subdirectory. Disable tests and
demos. Link to libcore to make it generally accessible and since the
meerkat upload will need it.

sirikata/sirikata,sirikata/sirikata,sirikata/sirikata,sirikata/sirikata,sirikata/sirikata,sirikata/sirikata,sirikata/sirikata,sirikata/sirikata