That parameter was introduced in cbcc2fa5 and removed in d22b78c8

This way we do not loose the context of the current page. Further, the
new id generated from the query before wasn't really that useful (see
issue #1124 ). And we can still generate a meaningful link "create a
page for your query", if that is considered useful.

Further redirects exist for the old urls, so bookmarked searches etc.
should mostly keep working.

This adds two new config options:

`search_limit_to_first_ns`:
Limit the search to the current X namespaces. When a search is executed
from a page within a deeper namespace, the first X namespaces will be
added as filter.
Possible use case could be with language namespaces to ensure that the
default search is initially within the current language.

`search_default_fragment_behaviour`:
Option to specify the default fragment search behavior

This commit should be without functional changes.

This is neither complete nor working, yet