Add JNI bindings for some of the libselinux interfaces.

Change-Id: Ifcc68cb06f9f56a04f3bc64dd9906a9436fabc88

Conflicts:
	core/java/android/os/SELinux.java
	core/jni/Android.mk
	core/jni/AndroidRuntime.cpp
	core/jni/android_os_SELinux.cpp