fix logic error with search filter.

if a post was in more than one different level, it would be hidden from search from ALL levels because the original query would ALWAYS return its ID since it's page_id would exist for a level other that the current user's level.

this update adds a second query to find the posts that ARE in the current users level and subtracts that from the original query.
Merge pull request #75 from normanyung/master

fix logic error with search filter.