get as .Internal; some related bug fixes

...n/src/com/oracle/truffle/r/nodes/builtin/base/DoCall.java

...ltin/src/com/oracle/truffle/r/nodes/builtin/base/Get.java

...iltin/src/com/oracle/truffle/r/nodes/builtin/base/R/get.R

...c/com/oracle/truffle/r/nodes/access/ReadVariableNode.java

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

...est/src/com/oracle/truffle/r/test/ExpectedTestOutput.test

...le.r.test/src/com/oracle/truffle/r/test/all/AllTests.java

...t/src/com/oracle/truffle/r/test/failing/FailingTests.java

.../com/oracle/truffle/r/test/simple/TestSimpleBuiltins.java

...com/oracle/truffle/r/test/simple/TestSimpleFunctions.java