More fixes for mongodb

Hi there, Antonin.

Here we have more fixes for the packaging, including patches to enable building on kFreeBSD, contributed by Jeff.

BTW, I would usually generate debian/changelog with something like `git-dch -S -a`, but I refrained from doing so because I am not sure what is your preferred workflow.

Well, that's it for now. It would be nice to have this hitting unstable soon, since once wheezy is released, the buildds will probably go crazy with an abundance of uploaded packages. :)