tests/test-diff-newlines.t

procutil: compare fd number to see if stdio protection is needed (issue5992)

When I wrote this function for commandserver at 69f86b937035, testing object
identity was suffice, and I was sloppy enough not to compare fileno() values.
However, it doesn't work in chg session because chgserver reopens stdio to
apply new buffering mode.

This patch partially fixes the issue 5992. Still we have another problem in
chgui._runsystem().

  $ hg init

  $ $PYTHON -c 'open("a", "wb").write(b"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