[PATCH] util: add allowhardlinks module variable

[Durham Goode]

On 3/2/17 10:12 AM, Durham Goode wrote:
> # HG changeset patch
> # User Durham Goode <durham at fb.com>
> # Date 1488476378 28800
> #      Thu Mar 02 09:39:38 2017 -0800
> # Node ID d52b0a72423f65b4f774d5b646474cdafd4a5cc0
> # Parent  a8458fe51a9d155f1daeaffdcf503e674d4d4588
> util: add allowhardlinks module variable
>
> To enable extensions to enable hardlinks for certain environments, let's move
> the 'if False' to be an 'if allowhardlinks' and let extensions modify the
> allowhardlinks variable.
>
> Tests on linux ext4 pass with it set to True and to False.

Sorry for the immediate V2.  I had uncommited working copy changes that 
I had forgotten to amend, so I had to send V2.