samples: add Terra samples

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

samples/Terra/forsym.t

@@ -0,0 +1,24 @@
+
+terra foo(a : int, s : int)
+    var r = 0
+    for i = 0,a,s do
+        r = r + i
+    end
+    return r
+end
+
+local i = symbol()
+
+terra foo2(a : int)
+    var r = 0
+    for [i] = 0,a do
+        r = r + [i]
+    end
+    return r
+end
+
+local test = require("test")
+test.eq(foo(10,1),45)
+test.eq(foo(10,2),20)
+test.eq(foo(0,1),0)
+test.eq(foo2(10),45)