Changes for nix-bisect

0.4.1 - 2020-04-09

Gracefully handle extra-bisect commands when no good or bad commit is provided yet.

Support for regular skip in the bisect runner. This is in addition to skip-range.
More reliable parsing of nix build error output.
Reuse of old skip-ranges when the cherry-picks that are supposed to unbreak them do not apply.
Patchsets are now persisted in the git tree, so the bisection can be aborted and resumed.
Nicer output in the bisect log.
High-Level Derivation interface.
Split of the CLI into nix-build-status, extra-bisect and bisect-env.
Make use of gcroots to prevent repeated builds.
Some builds can now be blacklisted so that they will always lead to skips.
Options and argstrings can be passed through to nix.

This is the first release with outside contributions. Thank you @bhipple and @lheckemann.

Successful cached builds are no longer unnecessarily fetched.
We now cache logs of failures, even dependency failures. This enables reliable skip caching (since nix log is not reliable) and transitive build failure caching (i.e. caching of dependency failures).
There is a new nix-bisect entrypoint which can be called directly instead of calling the python module.
The nix file to build an attribute from can now be changed by passing --nix-file or -f.
There is now a new (very experimental) bisect runner that can be enabled with the --bisect-runner flag. When that flag is used, nix-bisect should used standalone instead of as a parameter of git bisect. Taking full control of the bisection opens the door to many possible improvements.
One such improvement is already implemented: The bisect runner will treat skips as ranges (i.e. a commit between two skips is assumed to be skipped as well) and automatically identifies which commit "unbreak" this range. It then automatically cherry-picks those "unbreak" commits to enable further bisection.