When switching from main wiki to a sub wiki, the current user is wrong in URL path based multiwiki

To reproduce:

• go to main wiki
• login
• go to a sub wiki
  -> the user profile link point to a local user profile instead of the global user

This is because "one auth by session" feature does not see database switch but in normal multiwiki each wiki has its own domain and so its own cookie. In path based multiwiki the cookie remains the same so the auth is not rechecked and since the stored principal does not contains the wiki name it's wrong when in another wiki.