Next beta version towards 2.0.0 milestone

Hi,

we've got 4 PRs which are not WIP (2 x Windows fixes, 1 Debian packaging
and an improvement of the travis YAML), I'd like to merge them, switch
the Travis CI to `on.tag: true` and then generate the next beta tag.

By common request, I'd make the next tag v1.9.0b0 to make it clearer
that it's a beta before 2.0.0 (and the "b0" instead of beta will make
sure that tag and filename versions are the same).

If you disagree with any of this, or want to bring something before the
next beta, just shout on this mailing list.

KR, Eric