D476: util: add an mmapread method

[quark (Jun Wu)]

quark requested changes to this revision.
quark added a comment.
This revision now requires changes to proceed.


  Scanning staling patches - I think this patch is good after making fd work with both file object and file descriptor number.
  
  I will fix it in-place if you don't get it on Wednesday.

REPOSITORY
  rHG Mercurial

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

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