log: speed up hg log for untracked files (issue1340) 'hg log' on untracked files tends to be fairly slow. The root cause is that we end up using the 'slowpath' when we can't find a revlog for the files listed. This could happen if the file in question is an untracked file, or it is a directory. This diff tries to speed up 'hg log' (by avoiding the slowpath) for files if we can determine if that file is not (and was never) a directory. We use the previously added store.__contains__ methods to test if the directory exists (or existed) in the store. To avoid changing any existing semantics, this 'optimization' kicks in only when none of the files listed as arguments to the hg log command exist in the store.