r20844: Somewhat radical change - this may break the build (I will

r20844: Somewhat radical change - this may break the build (I will
watch carefully - so I'm doing it in one transaction so I can
roll back).

Change check_name(), reduce_name() and dptr_create() to
return NTSTATUS. This helps a lot in error path processing
and especially in reduce_name() allows us to ditch the flaky
and error-prone saving of errno and return errors directly.

Jeremy.
(This used to be commit 6133a694aa429d638320e39ffe1c49d172583ccf)