Add a check that we don't hide builtin module names with our tests

Also, move exceptions.py since that conflicts

tools/tester.py

@@ -412,6 +412,17 @@ if __name__ == "__main__":
             ]
     tests += big_tests
 
+    for t in tests:
+        bn = os.path.basename(t)
+        assert bn.endswith(".py")
+        module_name = bn[:-3]
+        try:
+            __import__(module_name)
+            raise Exception("Error: %s hides builtin module '%s'" % (t, module_name))
+        except ImportError:
+            pass
+            # good
+
     for t in TOSKIP:
         assert t in ("%s/t.py" % TEST_DIR, "%s/t2.py" % TEST_DIR) or t in tests, t