Fix the Jep.nodeToExpression method
|Reported by:||Nicklas Nordborg||Owned by:||Nicklas Nordborg|
It contains a lot of instanceof operations. Maybe we should register functions in a more flexible way so we can convert from a Jep function to a Query API expression for the standard functions just as we can for the extended functions (if the implement the JepExpressionFunction interface). If we want to support more function the current implementation needs to be changed in several places.