[ADD] XQuery, updated higher-order function signatures:
      http://docs.basex.org/wiki/Higher-Order_Functions
[MOD] Commands, XQuery: filename added to query info.
[ADD] XQuery, Database Module: db:name(), db:path(), db:export()
[MOD] XQuery, Database Module: functions no longer accept database nodes
      as reference. More: http://docs.basex.org/wiki/Database_Module
[FIX] GUI, Export dialog: parameter choice revised
[MIN] XQuery, better error feedback