make usages of ROptions.getValue able to deal with scalar values

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

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

...racle/truffle/r/nodes/builtin/base/PrettyPrinterNode.java

...truffle/r/nodes/builtin/base/printer/PrintParameters.java

.../truffle/r/nodes/builtin/helpers/BrowserInteractNode.java

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