Sanitize and limit tags in search to 10 (wincent.dev, c90d6d5)

Remove duplicate tags in search query and limit the total number to 10 to guard against attacks on the database. It is highly unlikely that a search with more than 10 tags would return any results anyway, given that the average number of tags per item is probably well under five.

Signed-off-by: Greg Hurrell <greg@hurrell.net>