We use it in router.c, where chunks are joined with "", not with
NL... so leaving off the terminating NL will lead to an unparseable
extrainfo.

Found by toralf. Bug not in any released Tor.

```
src/feature/stats/rephist.c: In function ‘overload_happened_recently’:
src/feature/stats/rephist.c:215:21: error: comparison between signed and unsigned integer expressions [-Werror=sign-compare]
   if (overload_time > approx_time() - 3600 * n_hours) {
```
from tpo/core/tor#40341 (comment 2729364)

This uses a heuristic that came up after a discussion with David.

I'm leaving this as a separate commit so that it can be discussed further if
needed.

- OOM metric
- onionskin overload metric
- DNS timeout metric

- Implement overload statistics structure.
- Implement function that keeps track of overload statistics.
- Implement function that writes overload statistics to descriptor.
- Unittest for the whole logic.

Nick Mathewson authored Mar 12, 2021 and David Goulet committed Mar 17, 2021

(If you need to do this in an older version you can just set
DormantClientTimeout to something huge.)

Closes #40228.

"ours" to avoid version bump.

"ours" to avoid version bump.

"ours" to avoid version bump.

(0.4.6.1-alpha will come out after the stable releases.)

We were looking for the first instance of "directory-signature "
when instead the correct behavior is to look for the first instance
of "directory-signature " at the start of a line.

Unfortunately, this can be exploited as to crash authorities while
they're voting.

Fixes #40316; bugfix on 0.2.2.4-alpha.  This is TROVE-2021-002,
also tracked as CVE-2021-28090.

We're going to disable this feature in all versions for now.