Fix input mappings being assigned to the wrong controller

In SDL 2, each joystick has a "device index" and an "instance ID", and at
least on Windows, they can be different numbers. We were trying to use
them interchangeably, and the result was that the control config menu
would disagree with the rest of the engine about which controller was
which.

Fixes #70

engine/sdl/control.c

@@ -171,11 +171,11 @@ void getPads(Uint8* keystate, Uint8* keystate_def)
 				break;
 
 			case SDL_JOYBUTTONDOWN:
-				// FIXME: restore GP2X controls
 				for(i=0; i<JOY_LIST_TOTAL; i++)
 				{
-					if(ev.jbutton.which == i)
+					if (SDL_JoystickInstanceID(joystick[i]) == ev.jbutton.which)
 					{
+						//printf("Button down: controller %i, button %i\n", i, ev.jbutton.button);
 						lastjoy = 1 + i * JOY_MAX_INPUTS + ev.jbutton.button;
 
 						// add key flag from event
@@ -189,7 +189,7 @@ void getPads(Uint8* keystate, Uint8* keystate_def)
 			case SDL_JOYHATMOTION:
 				for(i=0; i<JOY_LIST_TOTAL; i++)
 				{
-					if(ev.jhat.which == i)
+					if (SDL_JoystickInstanceID(joystick[i]) == ev.jhat.which)
 					{
 						int hatfirst = 1 + i * JOY_MAX_INPUTS + joysticks[i].NumButtons + 2*joysticks[i].NumAxes + 4*ev.jhat.hat;
 						x = (joysticks[i].Hats >> (4*ev.jhat.hat)) & 0x0F; // hat's previous state
@@ -213,7 +213,7 @@ void getPads(Uint8* keystate, Uint8* keystate_def)
 			case SDL_JOYAXISMOTION:
 				for(i=0; i<JOY_LIST_TOTAL; i++)
 				{
-					if(ev.jaxis.which == i)
+					if (SDL_JoystickInstanceID(joystick[i]) == ev.jaxis.which)
 					{
 						int axisfirst = 1 + i * JOY_MAX_INPUTS + joysticks[i].NumButtons + 2*ev.jaxis.axis;
 						x = (joysticks[i].Axes >> (2*ev.jaxis.axis)) & 0x03; // previous state of axis