support root-namespace parent classes

[staabm]

a file with content

<?php

class X {}

class Y extends X {}

class Z extends ArrayObject {}

is fixed into

<?php

final class X {}

final class Y extends X {}

final class Z extends ArrayObject {}

but I expected class X not to get final. Its hard to unit-test because all tests atm require a namespace.

Originally posted by @staabm in #19 (comment)