Update for current varnish-cache and polish

[nigoroll]

This makes the vmod work and pass the test-suite with varnish-cache as of baf60b4d2ef5f418e6ac470f3562e43c37e2ad44

Please see individual commit messages.

[gquintard]

looks good to me, but I don't have commit access anymore :-)

[gquintard]

@Dridi, @hermunn, unless there's an objection, I'm merging this next week

[dridi]

I object to @gquintard's definition of a week.

[gquintard]

merged, thanks @nigoroll !