Ubuntu LTS still uses jansson 2.2.1 in their repo and the code does in fact support 2.2.  The libs change was definitely my fault though, I forgot all about r7939.

git-svn-id: svn://svn.icculus.org/fs2open/trunk/fs2_open@9963 387891d4-d844-0410-90c0-e4c51a9137d3