Ensure that the version part of $_url_base is correctly removed by

Ensure that the version part of $_url_base is correctly removed by
using $VNAME (x.y) instead of $VERSION (xy). This fixes the problem
that the version part ended up in installurl which is wrong anyway
and also confuses pkg_add.

Thanks to florian@ and trondd at kagu-tsuchi dot com for reporting
this.

OK tb@