Recreate render target textures when the D3D device is being reset, and notify the application using the SDL_RENDER_TARGETS_RESET event when this happens.

include/SDL_events.h

@@ -134,6 +134,9 @@ typedef enum
     /* Drag and drop events */
     SDL_DROPFILE        = 0x1000, /**< The system requests a file open */
 
+    /* Render events */
+    SDL_RENDER_TARGETS_RESET = 0x2000, /**< The render targets have been reset */
+
     /** Events ::SDL_USEREVENT through ::SDL_LASTEVENT are for your use,
      *  and should be allocated with SDL_RegisterEvents()
      */