localrepo: introduce a `_quick_access_changeid` property
Having faster access to `null` is cute… but limited. We want to speedup access
to more useful revision, like `.`. We start with turning the fast path for
`null` into something more generic.
Differential Revision: https://phab.mercurial-scm.org/D7488
{
"version": 1,
"project": "mercurial",
"project_url": "https://mercurial-scm.org/",
"repo": "..",
"branches": ["default", "stable"],
"environment_type": "virtualenv",
"show_commit_url": "https://www.mercurial-scm.org/repo/hg/rev/",
"benchmark_dir": "benchmarks",
"env_dir": "../.asv/env",
"results_dir": "../.asv/results",
"html_dir": "../.asv/html"
}