The database isn't considered empty when installing the UI with DW

Steps to reproduce:

1. Unzip http://download.forge.ow2.org/xwiki/xwiki-enterprise-jetty-hsqldb-6.2.6.zip
2. Delete the "data" folder
3. Start XWiki -> you get the DW
4. Click Continue
5. On Step 1 of DW you get this message:

   Are you performing an upgrade? There are currently 4 documents in the database which indicates this is not a new install. Unfortunately we couldn't determine what version of the user interface was previously installed, most probably because you are upgrading from an old version that didn't have the distribution manager available.

even if the database should be empty.