As discussed on core enable the abstract class construction warning by default and also make it controllable with {$warn constructing_abstract ...}.

* scandir.pas, dir_warn: also adjust the message state for type_w_instance_abstract_class if the identifier is CONSTRUCTING_ABSTRACT
* msg/errore.msg: enable type_w_instance_abstract_class by default

* msgidx.inc, msgtxt.inc: updated


git-svn-id: http://svn.freepascal.org/svn/fpc/trunk@28137 3ad0048d-3df7-0310-abae-a5850022a9f2