use DOKU_URL as key for sessions and auth cookie #896 #581 #884

This patch changes the DOKU_COOKIE define to be based on the DOKU_URL define.
DOKU_COOKIE is now used as session key as well, making sessions no longer
dependend on the title option. This should fix problems with multiple
wikis on the same host (using the same title) and wikis accessed through
different URLs.

darcs-hash:20061003121546-7ad00-aea4c256b7752815ed422ce74a659152a601d267.gz