disable https->http redirects in libcurl

This change prevents changing the protocol from https to http.
test/integration/test-bug-723705-tagfile-truncates-fields: fix autopkgtest failure
simplify code some more to make reddit happy

Commit 6008b79adf1d7ea5607fab87a355d664c8725026 should have been guarded
by "Git-Dch: Ignore", but it wasn't and I only noticed it with the Close
message via deity thinking "hehe, I wonder if someone is gonna notice".
Looks like someone did: hats off to reddit user itisOmegakai!
Good to know that what I do isn't only monitored by goverments. :)

As there is another instance of basically the same code we just factor
out the code a bit and reuse, so its even cleaner and not only simpler.

Reported-By: scan-build
honor option to disable pulses for the testcases

Git-Dch: Ignore
add a testcase to check for forbidden https→http downgrades

Git-Dch: Ignore