Make Nextstep port handle multiple screens for resize and move.

Make Nextstep port handle multiple screens for resize and move.

* nsterm.h (ns_output): Add dont_constrain and zooming.
(EmacsView): Add ns_userRect.

* nsterm.m (keyDown): If ns_right_alternate_modifier is Qleft, check
if ns_alternate_modifier is none.

* nsterm.m (x_set_offset, windowDidMove): When calculating y, use first
screen, not the window screen.
(x_set_window_size): Remove constraints.
Calculate origin.y only if zooming is 0 and without referring to a
screen.
(windowWillResize): Don't modify frameSize.
(windowDidBecomeKey, mouseDown): Set dont_constrain to 1.
(initFrameFromEmacs): Initialize ns_userRect.
(windowShouldZoom): Set zooming to one.  Remove all other code.
(windowWillUseStandardFrame): Move static ns_userRect to EmacsView.
Zero it after restore.
(constrainFrameRect): New method for EmacsWindow.
(mouseDragged): Always post NSWindowDidResizeNotification after call to
windowWillResize.