Android compatibility fixes

Android compatibility fixes

* doc/emacs/android.texi (Android Windowing): Document
restrictions on number of windows under Android 4.4 and earlier.

* java/AndroidManifest.xml.in <EmacsActivity>
<EmacsOpenActivity, EmacsMultitaskActivity>: Assign each class
of activity a unique task affinity.

* java/org/gnu/emacs/EmacsDesktopNotification.java (display1):
Remove redundant priority assignment.

* java/org/gnu/emacs/EmacsOpenActivity.java (onCreate): Handle
file URIs when processing attachments from a mailto URI, and
check for KitKat before opening content ones.

* java/org/gnu/emacs/EmacsWindow.java <pointerMap>
(figureChange): Replace coordinate HashMap with a SparseArray.

* java/org/gnu/emacs/EmacsWindowAttachmentManager.java
(registerWindow): Don't specify FLAG_ACTIVITY_NEW_DOCUMENT on
systems where it is absent.