Hide duplicates in /tags/show_sentences_with_tag
Hide duplicates in /tags/show_sentences_with_tag

Solving #1331.
The database can currently have the same tag put several times on a
single sentence as a result of the deduplication process. This avoids
counting and displaying the same sentence as many times as it has
duplicate tags.

Tatoeba/tatoeba2,Tatoeba/tatoeba2,Tatoeba/tatoeba2,Tatoeba/tatoeba2,Tatoeba/tatoeba2