Final (?) update to declarednull branch

[Bart Schaefer <schaefer@brasslantern.com>]

This was pushed a few days ago but I was waiting to see if anyone
commented on the $empty[(i)] thread.  No one has, so I have left that
as it was.

The current tip of the declarednull branch in zsh git has added a test
script (E03) for the changes, leaving the original tests alone.  As
suggested elsewhere, the POSIXBUILTINS option enables this behavior.
There's exactly one test for this so it's easily swapped for some
other (new?) option.  That does mean, though, that you can do this:

() {
  typeset -ga zsharray
  setopt localoptions posixbuiltins
  typeset -ga posixarray
}
typeset -p zsharray posixarray
print $+zsharray $+posixarray

which yields

typeset -a zsharray=( )
typeset -a posixarray
1 0

Any further remarks from other maintainers?  If we're interested in
merging this, I'll post a complete patch for a reference X-Seq number.