added free function
Merge branch 'aql2' of https://github.com/triAGENS/ArangoDB into aql2
Merge branch 'aql2' of https://github.com/triAGENS/ArangoDB into aql2
Merge branch 'aql2' of https://github.com/triAGENS/ArangoDB into aql2
fixed filter removal optimizer rule