Allow vendors to tag version information to Tor
Currently we have no idea which vendors are responsible for which set of relays in the network, as we only have a
version tag in our descriptors.
It would be useful if a vendor could build tor with something like that:
./configure --vendor-name="debian" --vendor-version="0.3.5.2~deb1337" and our version string would become something like:
tor_version=0.3.5.2 vendor=debian vendor_version=0.3.5.2~deb1337 in some backwards compatible manner.