Fix compatibility issues with Android clipboards

* java/org/gnu/emacs/EmacsClipboard.java (getClipboardData):
Return an AssetFileDescriptor.

* java/org/gnu/emacs/EmacsContextMenu.java (onMenuItemClick):
Typo corrections in commentary.

* java/org/gnu/emacs/EmacsOpenActivity.java (onCreate): Raise
minimum version on which to read file descriptors from
ParcelFileDescriptor objects to Honeycomb.

* java/org/gnu/emacs/EmacsSdk11Clipboard.java
(getClipboardData): Return the asset file descriptor.

* java/org/gnu/emacs/EmacsSdk8Clipboard.java (getClipboardData):
Adjust return type to match.

* src/android.h (struct android_parcel_file_descriptor_class):
Move from androidselect.c.

* src/androidselect.c (fd_class): Export function.
(android_init_emacs_clipboard): Adjust signature of
getClipboardData.
(android_init_asset_file_descriptor, close_asset_fd)
(extract_fd_offsets): New functions.
(Fandroid_get_clipboard_data): Extract file descriptor and
offset from the AssetFileDescriptor here, rather than in
getClipboardData.
(init_androidselect): Call android_init_asset_file_descriptor.

* src/androidvfs.c (android_init_fd_class): Export and enable
calling this function more than once.

java/org/gnu/emacs/EmacsOpenActivity.java

@@ -19,29 +19,23 @@ along with GNU Emacs.  If not, see <https://www.gnu.org/licenses/>.  */
 
 package org.gnu.emacs;
 
-/* This class makes the Emacs server work reasonably on Android.
+/* Opening external documents on Android.
 
-   There is no way to make the Unix socket publicly available on
-   Android.
+   This activity is registered as an application capable of opening text
+   files and files in several other formats that Emacs understands, and
+   assumes responsibility for deriving file names from the files
+   provided to `onCreate', potentially copying them to temporary
+   directories in the process, and invoking `emacsclient' with suitable
+   arguments to open the same.  In this respect, it fills the role of
+   `etc/emacs.desktop' on XDG systems.
 
-   Instead, this activity tries to connect to the Emacs server, to
-   make it open files the system asks Emacs to open, and to emulate
-   some reasonable behavior when Emacs has not yet started.
+   It is also registered as a handler for mailto URIs, in which capacity
+   it constructs invocations of `emacsclient' so as to start
+   `message-mailto' with their contents and attachments, much like
+   `etc/emacs-mail.desktop'.
 
-   First, Emacs registers itself as an application that can open text
-   and image files.
-
-   Then, when the user is asked to open a file and selects ``Emacs''
-   as the application that will open the file, the system pops up a
-   window, this activity, and calls the `onCreate' function.
-
-   `onCreate' then tries very to find the file name of the file that
-   was selected, and give it to emacsclient.
-
-   If emacsclient successfully opens the file, then this activity
-   starts EmacsActivity (to bring it on to the screen); otherwise, it
-   displays the output of emacsclient or any error message that occurs
-   and exits.  */
+   As with all other activities, it is registered in the package
+   manifest file.  */
 
 import android.app.AlertDialog;
 import android.app.Activity;
@@ -628,11 +622,12 @@ public final class EmacsOpenActivity extends Activity
 
 	    if (scheme.equals ("content")
 		/* Retrieving the native file descriptor of a
-		   ParcelFileDescriptor requires Honeycomb, and
+		   ParcelFileDescriptor requires Honeycomb MR1, and
 		   proceeding without this capability is pointless on
 		   systems before KitKat, since Emacs doesn't support
 		   opening content files on those.  */
-		&& Build.VERSION.SDK_INT >= Build.VERSION_CODES.HONEYCOMB)
+		&& (Build.VERSION.SDK_INT
+		    >= Build.VERSION_CODES.HONEYCOMB_MR1))
 	      {
 		/* This is one of the annoying Android ``content''
 		   URIs.  Most of the time, there is actually an