Update libotr to version 4.0.0

I've done two things:
1. added a version string to the old libotr-version (3.2.0)
2. updated the libotr-Formula to version 4.0.0

I don't know if the first step is senseless - but i think it won't break anything and so it's more consistent.

Only tested on my Mountain-Lion iMac here. Installs like a charm.