[Mac, OpenGLWindow] Wrong mouse position reported in mouse move callback

[syoyo]

This only happens on Mac.

https://github.com/bulletphysics/bullet3/blob/master/examples/OpenGLWindow/MacOpenGLWindow.mm#L946

Once the mouse position goes the outside of app window(created by OpenGLWindow), it then reports the mouse position based on root window, not relative to app window.

Here is the fix.

            // http://stackoverflow.com/questions/4630509/how-to-find-if-the-mouse-is-over-a-view
            NSPoint globalLocation = [ NSEvent mouseLocation ];
            NSPoint windowLocation = [ [m_internalData->m_myview window] convertScreenToBase:globalLocation ];
            NSPoint viewLocation = [ m_internalData->m_myview convertPoint:windowLocation fromView: nil ];

            NSPoint center = viewLocation;
            m_mouseX = center.x;
            m_mouseY = [m_internalData->m_myview GetWindowHeight] - center.y;

            // Add window boundary check if required.

Similar fix may also be required for mouse press event.