We need to set "Sandbox 0", until we fix sandbox errors that are
triggered by Ubuntu Xenial and Bionic. See 32722.

Part of 32240.

Require C99 standards-conforming code in Travis CI, but allow GNU gcc
extensions. Also activates clang's -Wtypedef-redefinition warnings.

Builds some jobs with -std=gnu99, and some jobs without.

Closes ticket 32500.

This reverts commit 511aeba8.

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.

We need to mitigate slow scheduling of Travis macOS jobs.

Closes ticket 32177.

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.

The jobs should be the same, but Travis may display them differently.

Part of 31859.

Frequently, when a patch fails, it has failures in several files.
Using the "-k" flag will let us learn all the compilation errors,
not just the first one that the compiler hits.

Based on a patch by rl1987.

This warning would previously be given every time we tried to open a
connection to a foo.exit address, which could potentially be used to
flood the logs.  Now, we don't allow this warning to appear more
than once every 15 minutes.

Fixes bug 31466; bugfix on 0.2.2.1-alpha, when .exit was first
deprecated.

We previously used tor_fragile_assert() to declare that this case
could not happen: VERSIONS cells are always supposed to be
variable-sized, right?

This is incorrect, though.  On a v1 link protocol connection, all
cells are fixed-sized.  There aren't supposed to be any VERSIONS
cells with this version of the protocol, but apparently, somebody
was messing up.  (The v1 link protocol is obsolete, so probably the
implementer responsible didn't mean to be using it.)

Fixes bug 31107.  Bugfix on 0.2.4.4-alpha, when we introduced a
tor_fragile_assert() for this case.

Closes #31673

New IP address from 194.109.206.212 to 45.66.33.45.

Signed request from Alex de Joode, operator of dizum:
https://trac.torproject.org/projects/tor/ticket/31406



Published descriptor by dizum on August 12th, 2019:

--
r dizum fqbq1v2DCDxTj0QDi7+gd1h911U GZmZtCLaPDQNxkhIFj8UcgTRAuA 2019-08-12 15:28:40 45.66.33.45 443 80
s Authority Fast Running Stable V2Dir Valid
v Tor 0.4.0.5
pr Cons=1-2 Desc=1-2 DirCache=1-2 HSDir=1-2 HSIntro=3-4 HSRend=1-2 Link=1-5 LinkAuth=1,3 Microdesc=1-2 Relay=1-2 Padding=1
w Bandwidth=20 Unmeasured=1
p reject 1-65535
--

Finally, confirmed by DNS:

  $ dig +short tor.dizum.com
  45.66.33.45

Closes #31406
Signed-off-by: David Goulet <dgoulet@torproject.org>

Fixes bug 31374; bugfix on 0.2.9.1-alpha.

My previous fix removed a comparison, which would have caused us to
warn about every skew instead of skews of over an hour.