tests/test-diff-issue2761.t

copyfile: add an optional parameter to copy other stat data

Contrary to the comment, I didn't see any evidence that we were copying
atime/mtime at all. This adds a parameter to copyfile to optionally copy it and
other stat data, with the default being to not copy it.

Many systems don't support changing the timestamp of a symlink, but we don't
need that in general anyway -- copystat is mostly useful for editors, most of
which will dereference symlinks anyway.

Test issue2761

  $ hg init

  $ touch to-be-deleted
  $ hg add
  adding to-be-deleted
  $ hg ci -m first
  $ echo a > to-be-deleted
  $ hg ci -m second
  $ rm to-be-deleted
  $ hg diff -r 0

Same issue, different code path

  $ hg up -C
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ touch does-not-exist-in-1
  $ hg add
  adding does-not-exist-in-1
  $ hg ci -m third
  $ rm does-not-exist-in-1
  $ hg diff -r 1