hgcia: Handle URL like in notify (issue2406) The URL must be composed with baseurl and webroot like in notify

util: make str(url) return file:/// for abs paths again str(url) was recently changed to return only file:/. However, the canonical way to represent absolute local paths is file:/// [1], which is also expected by at least hgsubversion. Relative paths are returned as file:the/relative/path. [1] http://en.wikipedia.org/wiki/File_URI_scheme