parse functions to RFunctions directly (without eval)

...fle.r.engine/src/com/oracle/truffle/r/engine/REngine.java

...truffle/r/nodes/builtin/base/HiddenInternalFunctions.java

...om/oracle/truffle/r/nodes/builtin/base/LoadFunctions.java

...acle/truffle/r/nodes/builtin/base/SerializeFunctions.java

...nodes/src/com/oracle/truffle/r/nodes/RTruffleVisitor.java

...acle/truffle/r/nodes/function/FunctionDefinitionNode.java

...acle/truffle/r/nodes/function/FunctionExpressionNode.java

....r.runtime/src/com/oracle/truffle/r/runtime/RContext.java

....runtime/src/com/oracle/truffle/r/runtime/RSerialize.java