Adds android example using jni.

examples/cross_calculator/android/scripts/jnibuild.sh

@@ -0,0 +1,22 @@
+#!/bin/sh
+
+# Force errors to fail script.
+set -e
+
+# If we are running from inside the scripts subdir, get out.
+if [ ! -d src ]
+then
+	cd ..
+fi
+
+# Ok, are we out now?
+if [ -d src ]
+then
+	javah -classpath bin/classes \
+		-o jni/backend-jni.h \
+		com.github.nimrod.crosscalculator.CrossCalculator
+else
+	echo "Uh oh, bin/classes directory not found?"
+	echo "Try compiling your java code, or opening in eclipse."
+	exit 1
+fi