Add detection for pointers deallocated with naDelete when they get deleted twice

[Manderby]

Deallocation using naRelease has this built in because of the NARefCount which is checked upon calling naRelease or naRetain. But naDelete does not have the storage capacity to do that.

Would need an additional dummy-space similar to the refcount but which is only available whe NA_DEBUG is 1.

When doing this, think about adding this functionality to all structs which use naClearXXX. Maybe do something with NAPtr