Added support for code block as argument to assert_same
Code block can return result or raise exception.

Examples:

    assert_same(<<-END) do
        foo
    END
        # Code block starts here
        a = "foo"
    end

    assert_same(<<-END) do
        Exception NoMethodError: undefined method `+' for nil:NilClass
    END
        # Code block starts here
        nil + 1
    end