Fixing anonymous user being able to RW with any ACL setting.

If we don't have this, the anonymous user will be checked in ___read_from_sections__ against one of the following regex:
```python
    "owner_write": "[r]\nuser:.*\ncollection:.*\npermission:r\n"
```
or:
```python
    "owner_only": "[rw]\nuser:.*\ncollection:^%(login)s/.+$\npermission:rw",
```

via:
```python
    user_match = re.match(re_user, user)
```

Now since an anonymous user means:
* __user == None__ in __authorized(user,collection, right)__, 
* and __user == ""__ in ___read_from_sections(user,collection, permission)__,

__re.match(".*", "")__ will always return __True__, giving at least the read permission for anonymous users.

Here we bypass the ___read_from_sections__ process, as it was intented by:

```python
  return (
      rights_type == "none" or
  ...
```

If __rights_type__ is not __'none'__, then there is no reason for us to check permissions for an unauthenticated user.

/!\ Warning /!\: this may break current working configuration, since during my tests I could see that my calendar client (Kmail) first tries to anonymously fetch the collections, and will only provide authentication if it gets bumped. So as of now, users with insufficient permissions or wrong passwords are able to fetch collections, but if you apply this fix, users with insufficient permissions or wrong passwords will result in being unable to fetch the collections (which should be the correct behavior).