samples: add Terra samples

source: https://github.com/zdevito/terra/tree/master/tests

samples/Terra/terracast.t

@@ -0,0 +1,15 @@
+
+
+
+function addone(a)
+	return a + 1
+end
+
+
+local a1 = terralib.cast(int -> int, addone)
+
+terra dofn(a : int -> int)
+	return a(3)
+end
+local test = require("test")
+test.eq(dofn(a1),4)