Keep connections open by default again.

Reworking 3f09b1c6c0402235e1e4b8719a134f49d9c40766 after https://github.com/jenkinsci/subversion-plugin/commit/3f09b1c6c0402235e1e4b8719a134f49d9c40766#commitcomment-5152466 et seqq.