Fix #729; constant names are incorrect with 'define'

With this commit we fix the way namespace and name are combined to get a correct
constant name in the Constant Descriptor. This is a tandem commit with
https://github.com/phpDocumentor/Reflection/commit/10f0b570166e5d508db36d8c35ff5b44c6785b82,
which fixes a bug in the Reflection library.