Loosen netbsd package version parsing

Recently netbsd changed its tor version to "0.3.5.8nb2"...

  http://pkgsrc.se/net/tor

Clearly the 'nb2' suffix isn't part of our upstream version. I'm not entirely
sure what it means (maybe a re-packaging of 0.3.5.8?). Adjusting the version
parsing I use for netbsd to ignore it.