Update lang/onyx port to version 5.1.0. This is a bugfix release. The only
significant changes with respect to this port are:
* Documentation has been moved to the proper location
($PREFIX/share/onyx/doc --> $PREFIX/share/doc/onyx).
* pkg-plist has been fixed to include some files that were not listed. It
seems that the pkg-plist diff for the previous submission were not