initial implemention of using a view of "UNION ALL" instead of selecting the facts parent table (which causes several locks)
can't use readonly transactions when creating temporary view
properly alias the selected_facts view as facts1, facts2, etc.
use a WITH clause instead of a session modifier
WITH clauses don't allow restrictions to be pushed down, so use subquery expressions instead
intendation
use proper alias name
don't throw syntax exception if no corpus is selected
use the new corpus selection subquery also in matrix
use the new corpus selection subquery also in frequency sql generation
fix #357 (ANNIS locks too many tables if querying multiple corpora)