MAI: pass debuglog to ply.yacc.yacc only if debug

because otherwise `ply` will log messages.
This approach is similar to the method `astutils.ply.Parser.build`.

promela/yacc.py

@@ -77,7 +77,7 @@ def build(self, tabmodule=None, outputdir='', write_tables=False,
         """
         if tabmodule is None:
             tabmodule = self.tabmodule
-        if debuglog is None:
+        if debug and debuglog is None:
             debuglog = self.logger
         self.parser = ply.yacc.yacc(
             method='LALR',