Fixed run_sql_cached() to take into account the case of empty supplied list of affected tables.  This is useful to speed up "never-changing" SELECT queries even more.  Updated docstring.
Fixed run_sql_cached() to take into account the case of empty supplied
list of affected tables.  This is useful to speed up "never-changing"
SELECT queries even more.  Updated docstring.

tiborsimko/invenio,tiborsimko/invenio,inveniosoftware/invenio,inveniosoftware/invenio