Mac: Fix error message for haptic subsystem.

We were calling SDL_Error instead of SDL_SetError when the haptic subsystem
wasn't initialized.
Mac: Improve moving relative mode windows.

This makes it possible to move windows by their title bar, even if they're in
relative mode, if you click the title bar when the window does not have focus.

Bug: https://bugzilla.libsdl.org/show_bug.cgi?id=2396

--HG--
extra : amend_source : 01cfe87acac88dd75b2f074d3833129605c46ed2