Add a smaller version of the polymorphism.py microbenchmark, which is currently crashing

test/tests/polymorphism_small.py

+class Union(object):
+    def __init__(self, subs):
+        self.subs = subs
+
+    def score(self):
+        t = 0
+        for s in self.subs:
+            t += s.score()
+        t /= len(self.subs) ** 2.0
+        return t
+
+class Simple(object):
+    def score(self):
+        return 1.0
+
+class Poly1(object):
+    def __init__(self, sub):
+        self.sub = sub
+
+    def score(self):
+        return self.sub.score()
+
+d = 0.0
+def rand():
+    # Almost cryptographically secure?
+    global d
+    d = (d * 1.24591 + .195) % 1
+    return d
+
+def make_random(x):
+    if rand() > x:
+        return Simple()
+
+    if rand() < 0.3:
+        return Union([make_random(0.5 * x - 1), make_random(0.5 * x - 1)])
+    return Poly1(make_random(x - 1))
+
+print make_random(1000).score()