Import views ignores validation.

Hi,

This problem is happening, when I try to import a view with existing name. It only happens when original view wasn't saved into db (i.e. in code). We should always show validation message, if "Replace an existing view if one exists with the same name" isn't ticked.

Looks like https://www.drupal.org/node/421842 overlooked to validate the possibility that default views could get overwritten with a new imported view and that it wasn't intentional.