Force genexpr's signature to be noargs, fix ticket #720

--HG--
extra : transplant_source : %B1-f%40%DD%BE/jp%D6%1F%C8I%9C%C3%7D%7DL%FC%00

Cython/Compiler/ExprNodes.py

@@ -24,6 +24,7 @@ from Nodes import Node
 import PyrexTypes
 from PyrexTypes import py_object_type, c_long_type, typecast, error_type, \
      unspecified_type
+import TypeSlots
 from Builtin import list_type, tuple_type, set_type, dict_type, \
      unicode_type, str_type, bytes_type, type_type
 import Builtin
@@ -5251,6 +5252,8 @@ class GeneratorExpressionNode(LambdaNode):
     def analyse_declarations(self, env):
         self.def_node.no_assignment_synthesis = True
         self.def_node.analyse_declarations(env)
+        # Force genexpr signature
+        self.def_node.entry.signature = TypeSlots.pyfunction_noargs
         env.add_lambda_def(self.def_node)
 
     def generate_result_code(self, code):