samples: add Terra samples

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

samples/Terra/clean.t

@@ -0,0 +1,17 @@
+local c = terralib.includec("stdio.h")
+
+iamclean = macro(function(arg)
+    return quote
+        var a = 3
+        return a,arg
+    end
+end)
+    
+terra doit()
+    var a = 4
+    iamclean(a)
+end
+
+local a = doit()
+local test = require("test")
+test.meq({3,4}, a)