[INTERNAL] QGram Index: added a define to switch between trie and tree-like edge label
[INTERNAL] QGram Index: disable BucketRefinement spec if tree-like edge labels have been enabled
[INTERNAL] Masai: enabled tree-like qgram labels
[FIX] BucketRefinement QGram Index: fixed open()
Merge pull request #358 from esiragusa/fix/qgram

Small QGram VSTree fixes