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.

src/core/windows/SDL_windows.c

@@ -0,0 +1,67 @@
+/*
+  Simple DirectMedia Layer
+  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, subject to the following restrictions:
+
+  1. The origin of this software must not be misrepresented; you must not
+     claim that you wrote the original software. If you use this software
+     in a product, an acknowledgment in the product documentation would be
+     appreciated but is not required.
+  2. Altered source versions must be plainly marked as such, and must not be
+     misrepresented as being the original software.
+  3. This notice may not be removed or altered from any source distribution.
+*/
+#include "SDL_config.h"
+
+#ifdef __WIN32__
+
+#include "SDL_error.h"
+#include "SDL_windows.h"
+#include "SDL_assert.h"
+
+#include <objbase.h>  /* for CoInitialize/CoUninitialize */
+
+/* Sets an error message based on GetLastError() */
+int
+WIN_SetError(const char *prefix)
+{
+    TCHAR buffer[1024];
+    char *message;
+    FormatMessage(FORMAT_MESSAGE_FROM_SYSTEM, NULL, GetLastError(), 0,
+                  buffer, SDL_arraysize(buffer), NULL);
+    message = WIN_StringToUTF8(buffer);
+    SDL_SetError("%s%s%s", prefix ? prefix : "", prefix ? ": " : "", message);
+    SDL_free(message);
+    return -1;
+}
+
+HRESULT
+WIN_CoInitialize(void)
+{
+    const HRESULT hr = CoInitialize(NULL);
+
+    /* S_FALSE means success, but someone else already initialized. */
+    /* You still need to call CoUninitialize in this case! */
+    if (hr == S_FALSE) {
+        return S_OK;
+    }
+
+    return hr;
+}
+
+void
+WIN_CoUninitialize(void)
+{
+    CoUninitialize();
+}
+
+#endif /* __WIN32__ */
+
+/* vi: set ts=4 sw=4 expandtab: */