Changes

NEWT Multi-Monitor 1/2: Allow negative window position; Validate Screen-Index;

- Allow negative window position, using flag 'autoPosition' to mark a custom user position.
  This impacts Windows and X11 window creation code, which supports native auto positioning.

- Screen: Validate Screen-Index.
  In 'big-desktop' mode the Screen index is always 0. This is true for X11 with
  Xinerama enabled and MS-Windows in general.
  Platforms w/o multiple Screen support always use index 0.

- X11: Separate X11 Display/Screen/Window native code in their respective C files

- Windows test scripts: use '%*' to catch all arguments

- Add missing (c)