Fixes #2022, do not resume on Android when surfaceChanged

If the app is in landscape mode and the user presses the power button, a pause
is followed immediately by a surfaceChanged event because the lock screen
is shown in portrait mode. This triggers a "false" resume.
So, we just pause and resume following the onWindowFocusChanged events.

Also, wait for SDL_APP_WILLENTERBACKGROUND and SDL_APP_DIDENTERBACKGROUND before
blocking the event pump.

test/testloadso.c

@@ -0,0 +1,82 @@
+/*
+  Copyright (C) 1997-2013 Sam Lantinga <slouken@libsdl.org>
+
+  This software is provided 'as-is', without any express or implied
+  warranty.  In no event will the authors be held liable for any damages
+  arising from the use of this software.
+
+  Permission is granted to anyone to use this software for any purpose,
+  including commercial applications, and to alter it and redistribute it
+  freely.
+*/
+
+/* Test program to test dynamic loading with the loadso subsystem.
+*/
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+#include "SDL.h"
+
+typedef int (*fntype) (const char *);
+
+int
+main(int argc, char *argv[])
+{
+    int retval = 0;
+    int hello = 0;
+    const char *libname = NULL;
+    const char *symname = NULL;
+    void *lib = NULL;
+    fntype fn = NULL;
+
+    if (argc != 3) {
+        const char *app = argv[0];
+        fprintf(stderr, "USAGE: %s <library> <functionname>\n", app);
+        fprintf(stderr, "       %s --hello <lib with puts()>\n", app);
+        return 1;
+    }
+
+    /* Initialize SDL */
+    if (SDL_Init(0) < 0) {
+        fprintf(stderr, "Couldn't initialize SDL: %s\n", SDL_GetError());
+        return 2;
+    }
+
+    if (strcmp(argv[1], "--hello") == 0) {
+        hello = 1;
+        libname = argv[2];
+        symname = "puts";
+    } else {
+        libname = argv[1];
+        symname = argv[2];
+    }
+
+    lib = SDL_LoadObject(libname);
+    if (lib == NULL) {
+        fprintf(stderr, "SDL_LoadObject('%s') failed: %s\n",
+                libname, SDL_GetError());
+        retval = 3;
+    } else {
+        fn = (fntype) SDL_LoadFunction(lib, symname);
+        if (fn == NULL) {
+            fprintf(stderr, "SDL_LoadFunction('%s') failed: %s\n",
+                    symname, SDL_GetError());
+            retval = 4;
+        } else {
+            printf("Found %s in %s at %p\n", symname, libname, fn);
+            if (hello) {
+                printf("Calling function...\n");
+                fflush(stdout);
+                fn("     HELLO, WORLD!\n");
+                printf("...apparently, we survived.  :)\n");
+                printf("Unloading library...\n");
+                fflush(stdout);
+            }
+        }
+        SDL_UnloadObject(lib);
+    }
+    SDL_Quit();
+    return retval;
+}