Disable hardware acceleration on Android

It serves no purpose and causes tearing.  Uploading the bitmap
to the GPU takes about as long as it does to incrementally
update the surface in software.

* java/AndroidManifest.xml.in: Disable hardware acceleration.
* java/org/gnu/emacs/EmacsActivity.java (EmacsActivity): Make
lastClosedMenu static.
* java/org/gnu/emacs/EmacsDialog.java (toAlertDialog): Enable
hardware acceleration within alert dialogs.
* java/org/gnu/emacs/EmacsSurfaceView.java (onDraw): Describe
why hardware acceleration is disabled.
* java/org/gnu/emacs/EmacsWindow.java (run): Remove redundant
call.

java/org/gnu/emacs/EmacsSurfaceView.java

@@ -176,7 +176,25 @@ public final class EmacsSurfaceView extends View
   onDraw (Canvas canvas)
   {
     /* Paint the view's bitmap; the bitmap might be recycled right
-       now.  */
+       now.
+
+       Hardware acceleration is disabled in AndroidManifest.xml to
+       prevent Android from uploading the front buffer to the GPU from
+       a separate thread.  This is important for two reasons: first,
+       the GPU command queue uses a massive amount of memory (dozens
+       of MiB) to upload bitmaps to the GPU, regardless of how much of
+       the bitmap has actually changed.
+
+       Secondly, asynchronous texturization leads to race conditions
+       when a buffer swap occurs before the front buffer is fully
+       uploaded to the GPU.  Normally, only slight and tolerable
+       tearing should result from this behavior, but Android does not
+       properly interlock the ``generation ID'' used to avoid
+       texturizing unchanged bitmaps with the bitmap contents,
+       consequentially leading to textures in an incomplete state
+       remaining in use to the GPU if a buffer swap happens between
+       the image data being uploaded and the ``generation ID'' being
+       read.  */
 
     if (frontBuffer != null)
       canvas.drawBitmap (frontBuffer, 0f, 0f, uiThreadPaint);