remotefilelog: tell runbgcommand to not block on child process startup
These two invocations will always find a binary because they're
re-running hg. As a result, we can skip waiting for the subprocess to
start running and save a little bit of wall-time.
Differential Revision: https://phab.mercurial-scm.org/D6539
Set up
$ hg init repo
$ cd repo
Try to import an empty patch
$ hg import --no-commit - <<EOF
> EOF
applying patch from stdin
abort: stdin: no diffs found
[255]
No dirstate backups are left behind
$ ls .hg/dirstate* | sort
.hg/dirstate