Fix: Do not access RContext.getInstance() directly in main thread.

...oracle/truffle/r/engine/shell/EmbeddedConsoleHandler.java

.../oracle/truffle/r/engine/shell/JLineConsoleCompleter.java

...om/oracle/truffle/r/engine/shell/JLineConsoleHandler.java

...ngine/src/com/oracle/truffle/r/engine/shell/RCommand.java

...m/oracle/truffle/r/engine/shell/StringConsoleHandler.java

...e.r.runtime/src/com/oracle/truffle/r/runtime/RSource.java

.../com/oracle/truffle/r/runtime/context/ConsoleHandler.java

...src/com/oracle/truffle/r/runtime/context/ContextInfo.java

...acle/truffle/r/runtime/context/DefaultConsoleHandler.java

...ruffle/r/test/engine/shell/TestJLineConsoleCompleter.java

.../src/com/oracle/truffle/r/test/generate/FastRSession.java