Hi!
I'm the author behind the changes you are discussing.
Emacs 24.3 demonstrates a number of problems when you want to stretch Emacs across two screens and also when placing the title bar above the top of the screen (which is very useful when `ns-auto-hide-menu-bar' is non-nil). Applying the suggested patch would only reintroduce those problems.
A better solution would be to add to code to check if the Emacs frame is outside any monitor, and then (and only then) call the constrainFrameRect method of the parent class.
Also, if I remember correctly, 24.3 behaved differently when you had one monitor compared to multiple monitors. I removed this, as I didn't see the point of it, and because if introduced an extra level of complexity when it came to testing.
When it comes to `display-pixel-width', it should return the combined width of side-by-side monitors, so 24.4 and newer Emacs versions behave correctly.
I have attached a test file I used when I worked with the NS port.
Anyway, I'm glad that you have looked into this. The number of people actively working on the NS port are close to zero (I threw in the towel about a year ago, simply because I couldn't find the time I needed to spend on it). If you are interested in contributing, you can look at the "NeXTstep port" section of the "TODO" file.
-- Anders
ns-frame-test.el