Use "UNKNOWN" in omego if no yaclifw present

Since setup.py has a dependency on yaclifw,
there's no way for setup.py to auto-install
it. This fallsback to using "UNKNOWN" if no
yaclifw is present.
Merge pull request #42 from joshmoore/yaclifw-version-fix

Use "UNKNOWN" in omego if no yaclifw present