fix context-sensitivity of TruffleVM.eval, add TruffleTck tests for FastR

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

...ine/src/com/oracle/truffle/r/engine/TruffleRLanguage.java

...e/truffle/r/nodes/access/WriteLocalFrameVariableNode.java

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

....test/src/com/oracle/truffle/r/test/tck/FastRTckTest.java

mx.fastr/mx_fastr.py

mx.fastr/suite.py