operators are RSyntaxLookup instead of RSyntaxElement (in OperatorNode)

.../com/oracle/truffle/r/nodes/control/AbstractLoopNode.java

...des/src/com/oracle/truffle/r/nodes/control/BlockNode.java

....nodes/src/com/oracle/truffle/r/nodes/control/IfNode.java

...odes/src/com/oracle/truffle/r/nodes/control/NextNode.java

.../src/com/oracle/truffle/r/nodes/control/OperatorNode.java

...es/src/com/oracle/truffle/r/nodes/control/RepeatNode.java

...c/com/oracle/truffle/r/nodes/control/ReplacementNode.java

...des/src/com/oracle/truffle/r/nodes/control/WhileNode.java

...racle/truffle/r/nodes/function/signature/MissingNode.java