Re-fix stray attributes bug, and make a unit test for it.

lib/python/TAL/CHANGES.txt

@@ -10,4 +10,5 @@ TAL changes
 
       Bugs Fixed
 
-
+        - tal:atributes was creating stray attributes in METAL
+          expansion, and there was no unit test for this behavior.

lib/python/TAL/TALInterpreter.py

@@ -329,7 +329,7 @@ class TALInterpreter:
 
     def attrAction(self, item):
         name, value, action = item[:3]
-        if action > 1 and not self.showtal:
+        if action == 1 or (action > 1 and not self.showtal):
             return 0, name, value
         ok = 1
         if action == 2 and self.metal:

lib/python/TAL/tests/input/test_metal3.html

+<span tal:attributes="class string:foo">Should not get attr in metal</span>

lib/python/TAL/tests/output/test_metal3.html

+<span tal:attributes="class string:foo">Should not get attr in metal</span>