Infer a --repository argument from command arguments when reasonable.
In particular: if invoked without -R from a CWD not inside a repo, having been
passed one or more file paths as command arguments, where the nearest enclosing
repo of all of those paths is the same, quietly infer a -R option for that repo.
Otherwise abort with an error message as before.
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
removing b
abort: update spans branches, use 'hg merge' or 'hg update -C' to lose changes