InsertBefore fails with decorators

[MementoRC]

The decorators are not pulled-in with the definition:

    INPUT_SOURCE = """
        @decorate
        def test():
            test_this()"""

    EXPECTED_SOURCE = """
        await async_test()
        @decorate
        def test():
            test_this()"""

   ACTUAL_SOURCE = """
        @decorate
        await async_test()
        def test():
            test_this()"""

[MementoRC]

This does not seem to be easily solved without pulling in PR: #71