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/testmessage.c

@@ -0,0 +1,183 @@
+/*
+  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.
+*/
+
+/* Simple test of the SDL MessageBox API*/
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <signal.h>
+
+#include "SDL.h"
+#include "SDL_thread.h"
+
+static int alive = 0;
+
+/* Call this instead of exit(), so we can clean up SDL: atexit() is evil. */
+static void
+quit(int rc)
+{
+    SDL_Quit();
+    exit(rc);
+}
+
+static int
+button_messagebox(void *eventNumber)
+{
+    const SDL_MessageBoxButtonData buttons[] = {
+        {
+            SDL_MESSAGEBOX_BUTTON_RETURNKEY_DEFAULT,
+            0,
+            "OK"
+        },{
+            SDL_MESSAGEBOX_BUTTON_ESCAPEKEY_DEFAULT,
+            1,
+            "Cancel"
+        },
+    };
+
+    SDL_MessageBoxData data = {
+        SDL_MESSAGEBOX_INFORMATION,
+        NULL, // no parent window
+        "Custom MessageBox",
+        "This is a custom messagebox",
+        2,
+        buttons,
+        NULL // Default color scheme
+    };
+
+    int button = -1;
+    int success = 0;
+    if (eventNumber) {
+        data.message = "This is a custom messagebox from a background thread.";
+    }
+
+    success = SDL_ShowMessageBox(&data, &button);
+    if (success == -1) {
+        printf("Error Presenting MessageBox: %s\n", SDL_GetError());
+        if (eventNumber) {
+            SDL_UserEvent event;
+            event.type = (intptr_t)eventNumber;
+            SDL_PushEvent((SDL_Event*)&event);
+            return 1;
+        } else {
+            quit(2);
+        }
+    }
+    printf("Pressed button: %d, %s\n", button, button == 1 ? "Cancel" : "OK");
+
+    if (eventNumber) {
+        SDL_UserEvent event;
+        event.type = (intptr_t)eventNumber;
+        SDL_PushEvent((SDL_Event*)&event);
+    }
+
+    return 0;
+}
+
+int
+main(int argc, char *argv[])
+{
+    int success;
+
+    success = SDL_ShowSimpleMessageBox(SDL_MESSAGEBOX_ERROR,
+                "Simple MessageBox",
+                "This is a simple error MessageBox",
+                NULL);
+    if (success == -1) {
+        printf("Error Presenting MessageBox: %s\n", SDL_GetError());
+        quit(1);
+    }
+
+    success = SDL_ShowSimpleMessageBox(SDL_MESSAGEBOX_ERROR,
+                "Simple MessageBox",
+                "This is a simple MessageBox with a newline:\r\nHello world!",
+                NULL);
+    if (success == -1) {
+        printf("Error Presenting MessageBox: %s\n", SDL_GetError());
+        quit(1);
+    }
+
+    /* Google says this is Traditional Chinese for "beef with broccoli" */
+    success = SDL_ShowSimpleMessageBox(SDL_MESSAGEBOX_ERROR,
+                "UTF-8 Simple MessageBox",
+                "Unicode text: '牛肉西蘭花' ...",
+                NULL);
+    if (success == -1) {
+        printf("Error Presenting MessageBox: %s\n", SDL_GetError());
+        quit(1);
+    }
+
+    /* Google says this is Traditional Chinese for "beef with broccoli" */
+    success = SDL_ShowSimpleMessageBox(SDL_MESSAGEBOX_ERROR,
+                "UTF-8 Simple MessageBox",
+                "Unicode text and newline:\r\n'牛肉西蘭花'\n'牛肉西蘭花'",
+                NULL);
+    if (success == -1) {
+        printf("Error Presenting MessageBox: %s\n", SDL_GetError());
+        quit(1);
+    }
+
+    button_messagebox(NULL);
+
+    /* Test showing a message box from a background thread.
+
+       On Mac OS X, the video subsystem needs to be initialized for this
+       to work, since the message box events are dispatched by the Cocoa
+       subsystem on the main thread.
+     */
+    if (SDL_Init(SDL_INIT_VIDEO) < 0) {
+        fprintf(stderr, "Couldn't initialize SDL video subsystem: %s\n", SDL_GetError());
+        return (1);
+    }
+    {
+        int status = 0;
+        SDL_Event event;
+        intptr_t eventNumber = SDL_RegisterEvents(1);
+        SDL_Thread* thread = SDL_CreateThread(&button_messagebox, "MessageBox", (void*)eventNumber);
+
+        while (SDL_WaitEvent(&event))
+        {
+            if (event.type == eventNumber) {
+                break;
+            }
+        }
+
+        SDL_WaitThread(thread, &status);
+
+        printf("Message box thread return %i\n", status);
+    }
+
+    /* Test showing a message box with a parent window */
+    {
+        SDL_Event event;
+        SDL_Window *window = SDL_CreateWindow("Test", SDL_WINDOWPOS_CENTERED, SDL_WINDOWPOS_CENTERED, 640, 480, 0);
+
+        success = SDL_ShowSimpleMessageBox(SDL_MESSAGEBOX_ERROR,
+                    "Simple MessageBox",
+                    "This is a simple error MessageBox with a parent window",
+                    window);
+        if (success == -1) {
+            printf("Error Presenting MessageBox: %s\n", SDL_GetError());
+            quit(1);
+        }
+
+        while (SDL_WaitEvent(&event))
+        {
+            if (event.type == SDL_QUIT || event.type == SDL_KEYUP) {
+                break;
+            }
+        }
+    }
+
+    SDL_Quit();
+    return (0);
+}