By moving the tests subdirectory to t, we gain the ability to run `yath
test` with no arguments from inside `nix develop` in the root of the
the repo.
(`nix develop` is necessary in order to set the proper env vars for
`yath` to find our test libraries.)
This is caused by the autoconf check for `nix-store` which is equivalent
to running this:
```
$ nix-store --timeout 123 -q
```
This would open the pager on a 2.1.1 version of nix.
```
$ nix-store --version
nix-store (Nix) 2.1.1
```
Setting `PAGER` to `cat` ensures the pager doesn't block the
configurePhase.
```
$ PAGER=cat nix-store --timeout 123 -q
```
This rewrites the top-level loop of hydra-evaluator in C++. The Perl
stuff is moved into hydra-eval-jobset. (Rewriting the entire evaluator
would be nice but is a bit too much work.) The new version has some
advantages:
* It can run multiple jobset evaluations in parallel.
* It uses PostgreSQL notifications so it doesn't have to poll the
database. So if a jobset is triggered via the web interface or from
a GitHub / Bitbucket webhook, evaluation of the jobset will start
almost instantaneously (assuming the evaluator is not at its
concurrency limit).
* It imposes a timeout on evaluations. So if e.g. hydra-eval-jobset
hangs connecting to a Mercurial server, it will eventually be
killed.
It's easier for the Hydra provisioner to put host public keys in the
machines file than to separately manage the known_hosts file
(especially when the provisioner runs on a different machine).
The underscores are ugly and the .pl extension is an implementation
detail that shouldn't be visible to the outside.
Also, get rid of the *.in files. It's not really necessary to
generate them. And I was always modifying the wrong file.
Samuel Dionne-Riel