Update Android port

Update Android port

* doc/emacs/android.texi (Android Windowing): Document how to
pass multimedia keys to the system.
* java/org/gnu/emacs/EmacsNative.java (EmacsNative): New
function.
* java/org/gnu/emacs/EmacsView.java (onKeyDown, onKeyMultiple)
(onKeyUp): Check that function.
* java/org/gnu/emacs/EmacsWindow.java (defineCursor): Handle
cases where cursor is NULL.
* src/android.c (NATIVE_NAME): New function.
* src/androidfns.c (syms_of_androidfns): New variable.
* src/keyboard.c (lispy_function_keys): Add volume keys.