test-ancestor: define a main function

test-ancestor: define a main function

We're going to add to it in upcoming patches.

--- a/tests/test-ancestor.py	Fri Nov 14 14:50:03 2014 -0800
+++ b/tests/test-ancestor.py	Sat Nov 15 18:52:44 2014 -0800
@@ -132,7 +132,10 @@
                     print "  C returned:      %s" % cgcas
                     print "  Python returned: %s" % pygcas
 
-if __name__ == '__main__':
+def main():
     test_missingancestors()
     test_lazyancestors()
     test_gca()
+
+if __name__ == '__main__':
+    main()