Install the mingw OpenSSL package in Appveyor. This makes sure that
the OpenSSL headers and libraries match in Tor's Appveyor builds.

(This bug was triggered by an Appveyor image update.)

Fixes bug 32449; bugfix on 0.3.5.6-rc.

Bionic has a recent coccinelle version, which passes our CI tests.

But Bionic (and Xenial) cause permissions errors for chutney.
We'll fix those in 32240.

Part of 31919.

Closes ticket 32241.

`git merge --strategy ours` to take the 0.3.5 changes for 31001,
and ignore the conflicting 0.2.9 changes.

This build was added in 0.3.5.

We need to mitigate slow scheduling of Travis macOS jobs.

Closes ticket 32177.

Stem from maint-0.3.5, disabled macOS chutney from ticket32177_029.

We need to mitigate slow scheduling of Travis macOS jobs.

Closes ticket 32177.

Instead of Windows Server 2016.

Closes ticket 32086.

* actually sleep when tor has not logged anything
* log at debug level when waiting for tor to log something
* backslash-replace bad UTF-8 characters in logs
* format control messages as ASCII: tor does not accept UTF-8 control commands

Fixes bug 31837; bugfix on 0.3.5.1-alpha.

Since Rust on macOS is slow, don't wait for the macOS Rust job to finish.
Instead, split rust into slow rust (macOS) and fast rust (Linux). And
allow the build to finish before slow rust finishes.

Also make sure that we have:
* a Rust build on each platform,
* a Rust build with each compiler, and
* a check on all our Rust builds.

Finally, sort builds: allow fail last, macOS first, slowest first.

Closes 31859 for 0.3.5.

Part of 31859 for 0.3.5.

While merging:
* leave out some redundant jobs and build matrix entries

Since Travis macOS has IPv6 support (and Travis Linux does not), chutney
will now run its IPv6 networks as part of Travis CI.

But since chutney is slow, don't wait for the macOS chutney to finish.
(Travis have fixed the duplicate notification bug in fast_finish. So we
can use fast_finish and allow_failure to finish early. Unfortunately,
allow_failure also means we ignore failures in macOS chutney.)

Also make sure that we have:
* a compile on each platform, with each compiler,
* a check on each platform, and
* a check on each compiler.

Finally, sort builds: allow fail last, macOS first, slowest first.

Closes ticket 30860.
Closes ticket 31859 for 0.2.9.

Part of 31859.

When Appveyor fails before the install step, some of the finish step's
functions were not defined.

Fixes bug 31884; bugfix on 0.3.4.2-alpha.