Make buttonremap const and tweak comments

- fix right/middle button comments (swapped)
- add comments for left/back/forward buttons

Quake/in_sdl.c

@@ -80,13 +80,13 @@ static SDL_GameController *joy_active_controller = NULL;
 
 static qboolean	no_mouse = false;
 
-static int buttonremap[] =
+static const int buttonremap[] =
 {
-	K_MOUSE1,
-	K_MOUSE3,	/* right button		*/
-	K_MOUSE2,	/* middle button	*/
-	K_MOUSE4,
-	K_MOUSE5
+	K_MOUSE1,	/* left button		*/
+	K_MOUSE3,	/* middle button	*/
+	K_MOUSE2,	/* right button		*/
+	K_MOUSE4,	/* back button		*/
+	K_MOUSE5	/* forward button	*/
 };
 
 /* total accumulated mouse movement since last frame */