match: add the abs() method This is a utility to make it easier for subrepos to convert a file name to the full path rooted at the top repository. It can replace the various path joining lambdas, and doesn't require the prefix to be passed into the method that wishes to build such a path. The name is derived from the following pattern in annotate() and other places: name = ((pats and rel) or abs) The pathname separator is not os.sep in part to avoid confusion with variables named 'abs' or similar that _are_ '/' separated, and in part because some methods like cmdutils.forget() and maybe cmdutils.add() need to build a '/' separated path to the root repo. This can replace the manual path building there.