always initialize RContexts from ContextInfo

...gine/src/com/oracle/truffle/r/engine/RContextFactory.java

...rc/com/oracle/truffle/r/engine/RRuntimeASTAccessImpl.java

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

.../src/com/oracle/truffle/r/library/fastr/FastRContext.java

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

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

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

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

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