Revision 316431

Merge r315910:
  Make sendfile(2) more robust against file change.  This fixes a possible
  crash when the file shrinks.  This also fixes sendfile(2) not sending more
  data in a case when the file grows, and the request is open-ended or
  specifies a size that is greater than old file size.

  PR:           217789
  Reviewed by:  gallatin