tests/test-diff-newlines.t

copies: pass changectx instead of manifest to _computenonoverlap

The _computenonoverlap function takes two manifests to allow extensions to hook
in and read the manifest nodes produced by the function. The remotefilelog
extension actually needs the entire changectx instead (which includes the
manifest) so it can prefetch the subset of files necessary for a sparse checkout
(and the sparse checkout depends on which commit is being accessed, hence the
need for the changectx).

I have tests in the remotefilelog extension that cover this.

  $ hg init

  $ $PYTHON -c 'file("a", "wb").write("confuse str.splitlines\nembedded\rnewline\n")'
  $ hg ci -Ama -d '1 0'
  adding a

  $ echo clean diff >> a
  $ hg ci -mb -d '2 0'

  $ hg diff -r0 -r1
  diff -r 107ba6f817b5 -r 310ce7989cdc a
  --- a/a	Thu Jan 01 00:00:01 1970 +0000
  +++ b/a	Thu Jan 01 00:00:02 1970 +0000
  @@ -1,2 +1,3 @@
   confuse str.splitlines
   embedded\r (no-eol) (esc)
  newline
  +clean diff