rebase: also restore "ui.allowemptycommit" value
It looks like this was lost when the code was converted to the
ui.configoverride() context manager in
f255b1811f5e (rebase: get rid
of ui.backupconfig, 2017-03-16). (And then the bad example was
duplicated in
228916ca12b5 (rebase: add concludememorynode(), and call
it when rebasing in-memory, 2017-12-07).)
Differential Revision: https://phab.mercurial-scm.org/D2760
{
"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"
}