[PATCH RESEND] largefiles: speed up the check if largefiles should be added to repo requirements

[Dominik Psenner]

>this also signifies that we need largefiles

Actually: no. You don't require the largefiles extension until you actually
have .hglf in the store.

> and is faster than walking the store -- epsecially if the repo is large.

Yes, it would be. But again, it would add the largefiles requirement even if
it is not required yet. I.e.:

$ touch .hglf
$ hg st
$ hg revert
$ cat .hg/requirements
largefiles
**OPS**

>It won't help much in the I-have-largefiles-enabled-but-don't-use-
>them case

Instead it does. It checks the first level of files and folders in the store
(which is normally a quite small number of files and folders) and adds the
requirement once it finds .hglf there. We could discuss if we should not
walk the files and blindly guess the location of .hglf in the store, but as
said I was afraid from going that far. :-)

> but it will help in the "I-do-have-largefiles-enabled-and-I-do-
>use-them" case.

In this case largefiles are already in the requirements and we don't have to
add the requirement anymore.

Cheers,
D.