Fix 'next sentence' link
Fix 'next sentence' link

For some reason, CakePHP forces recursive to 0 in find('neighbors', ...)
(see Model::_findNeighbors()). As a result, related models are grabbed
when retrieving neighbor ids. Because the ReindexFlags model was mistakenly
linked as hasOne whereas it’s hasMany since ce10423dbd591d5c08e9382ce859d0,
the SQL join could unexpectingly result into more than one row for a single
sentence, effectively messing CakePHP’s neighbors retrieving algorithm.

Closes #1039.

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