Adding cython v0.20.2 in third-party.

third_party/cython/src/Cython/Debugging.py

Index: third_party/cython/src/Cython/Debugging.py
diff --git a/third_party/cython/src/Cython/Debugging.py b/third_party/cython/src/Cython/Debugging.py
new file mode 100644
index 0000000000000000000000000000000000000000..edb3f4e8ca582e4f0bc938c761b1fdf1f9d56f6b
--- /dev/null
+++ b/third_party/cython/src/Cython/Debugging.py
@@ -0,0 +1,20 @@
+###############################################
+#
+#   Odds and ends for debugging
+#
+###############################################
+
+def print_call_chain(*args):
+    import sys
+    print(" ".join(map(str, args)))
+    f = sys._getframe(1)
+    while f:
+        name = f.f_code.co_name
+        s = f.f_locals.get('self', None)
+        if s:
+            c = getattr(s, "__class__", None)
+            if c:
+                name = "%s.%s" % (c.__name__, name)
+        print("Called from: %s %s" % (name, f.f_lineno))
+        f = f.f_back
+    print("-" * 70)