D476: util: add an mmapread method

[simonfar (Simon Farnsworth)]

simonfar added inline comments.

INLINE COMMENTS

> util.py:413
> +    try:
> +        return mmap.mmap(fp.fileno(), 0, access=mmap.ACCESS_READ)
> +    except ValueError: # cannot mmap an empty file

As per comment on https://phab.mercurial-scm.org/D477 - do we want this to be raw, or `buffer(mmap.mmap(...`?

REPOSITORY
  rHG Mercurial

REVISION DETAIL
  https://phab.mercurial-scm.org/D476

To: mbthomas, #fbhgext, #hg-reviewers
Cc: simonfar, mercurial-devel