Dort behaviour change on php7 master

Hi all,

I just compiled master to test my main application and the good news is
that I have no functional regression and some of the views get a
considerable speed up (like, page generation divided by two!).

I had one unit test failing and I reduced that to a simple testcase that
I put there:

http://3v4l.org/4tGv6

Sorting in php master in this specific case is now different on PHP 7
than on 5.3-5.6 (and actually different than PHP 7 at the beginning of
the month). The sorting order is now the same as HHVM.

I think the HHVM behaviour makes more sense in this case as I don't see
why the resulting array should be reversed in this sorting case where
all lengths are equal, but on the other hand the current behaviour is
probably 10 years old and maybe it could cause bigger problems in other
apps than a unit test to update.

Just that you know, in case it matters.

Yeah, this is a known change and the documentation has had a note about
not relying on the ordering of equal elements. Although the note in the
manual is probably a bit too geeky. It should be more explicit and talk
about the effect rather than the cause:

Note: Like most PHP sorting functions, `sort()` uses an
      implementation of » Quicksort. The pivot is chosen in the
      middle of the partition resulting in an optimal time for
      already sorted arrays. This is however an implementation
      detail you shouldn't rely on.

-Rasmus