[PATCH 2 of 4 V2] largefiles: update largefiles in a subrepo when updating the parent (issue3752)

[Matt Harbison]

Benoit Boissinot wrote:
> FYI: I have a minimal fix for this, partly based on patch 2 from Matt,
> which should be suitable for the freeze.

Feel free to send.  I didn't mean to abandon this, but got busy for a 
few days and then sick, and it may be another day or two before I get 
back to this.  All I was going to do was the few tweaks Mads suggested 
(possibly without the clean filelist, but I wanted to dig into this 
first).  IIRC, there was something in there not suitable for stable, so 
your version might be better.

--Matt