[PATCH] largefiles: cache new largefiles for new heads when pulling

[Levi Bard]

> In order to do pretty much anything meaningful
> with another head (merge, rebase, or update to it), you will need to
> download these largefiles.

This is my rationale. This change also saves the user from having to
pass "--config paths.default=http://foo.bar.baz/some/repo/path" in
order to update to a new head.

> But I can imagine a situation, where you might not want this behavior -- if
> you have a huge number of named branches, for example, with several large,
> unique largefiles, and you are not sure when or if you will merge with any
> of them.

Perhaps, but this is far from the only situation where pulling all of
a huge number of named branches will do things irrelevant to whatever
branch in which a user happens to be interested.