Update Android port

Update Android port

* INSTALL.android: Explain how to build selinux.
* configure.ac: Enable selinux on Android.
* cross/ndk-build/ndk-build-shared-library.mk: ($(call
objname,$(LOCAL_MODULE),$(basename $(1))))::($$(error
Unsupported suffix)::(NDK_CFLAGS_$(LOCAL_MODULE)):
* cross/ndk-build/ndk-build-static-library.mk: ($(call
objname,$(LOCAL_MODULE),$(basename $(1))))::($$(error
Unsupported suffix)::(NDK_CFLAGS_$(LOCAL_MODULE)): Correctly
handle files with a .cc suffix, and clang-specific asflags.
* cross/ndk-build/ndk-clear-vars.mk: Handle AOSP extensions
LOCAL_ADDITIONAL_DEPENDENCIES,
LOCAL_CLANG_ASFLAGS_$(NDK_BUILD_ARCH) and LOCAL_IS_HOST_MODULE.

* doc/emacs/android.texi (Android Startup): Explain emacsclient
wrapper.

* java/org/gnu/emacs/EmacsView.java (EmacsView): New flag
`isCurrentlyTextEditor'.
(showOnScreenKeyboard, hideOnScreenKeyboard): Set as
appropriate.
(onCheckIsTextEditor): Return its value.

* lisp/touch-screen.el (touch-screen-handle-scroll): Don't ding
at buffer limits.
* m4/ndk-build.m4: Improve doc.

* src/Makefile.in (LIBSELINUX_CFLAGS): New variable.
(EMACS_CFLAGS): Add it.