Update Android port

* doc/lispref/commands.texi (Misc Events): Update documentation.
* java/org/gnu/emacs/EmacsService.java (EmacsService)
(onStartCommand): Improve notification message.
* src/android.c (android_hack_asset_fd): Detect if ashmem is
available dynamically.
(android_detect_ashmem): New function.
* src/textconv.c (record_buffer_change): Use markers to
represent BEG and END instead.
(syms_of_textconv): Update doc string.

java/org/gnu/emacs/EmacsService.java

@@ -101,6 +101,8 @@ public class EmacsService extends Service
   /* Display metrics used by font backends.  */
   public DisplayMetrics metrics;
 
+  /* Flag that says whether or not to print verbose debugging
+     information.  */
   public static final boolean DEBUG_IC = false;
 
   @Override
@@ -117,8 +119,10 @@ public class EmacsService extends Service
       {
 	tem = getSystemService (Context.NOTIFICATION_SERVICE);
 	manager = (NotificationManager) tem;
-	infoBlurb = ("See (emacs)Android Environment for more"
-		     + " details about this notification.");
+	infoBlurb = ("This notification is displayed to keep Emacs"
+		     + " running while it is in the background.  You"
+		     + " may disable if you want;"
+		     + " see (emacs)Android Environment.");
 	channel
 	  = new NotificationChannel ("emacs", "Emacs persistent notification",
 				     NotificationManager.IMPORTANCE_DEFAULT);