Be more strict about `//#else`

[Johni0702]

In particular, the following should not pass:

                    //#if MC>=12000
                    //$$ print(used1)
                    //#else#if MC>=11600
                    //$$ print(used2)
                    //#else
                    //$$ print(used3)
                    //#endif

Because

1. That's supposed to be an elseif but it was typo'd (current processor reads it as an else without complaints)
2. That's two else which probably shouldn't be legal