Fix compiler warnings.

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

...oracle/truffle/r/nodes/builtin/base/CompileFunctions.java

...com/oracle/truffle/r/nodes/builtin/base/EncodeString.java

...in/src/com/oracle/truffle/r/nodes/builtin/base/NChar.java

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

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

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

...cle/truffle/r/nodes/builtin/base/printer/ListPrinter.java

...ruffle/r/nodes/attributes/SpecialAttributesFunctions.java

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

...om/oracle/truffle/r/runtime/context/ChildContextInfo.java

.../com/oracle/truffle/r/runtime/data/nodes/GetDataCopy.java

...rc/com/oracle/truffle/r/runtime/data/nodes/SetDataAt.java

...e/src/com/oracle/truffle/r/runtime/nmath/distr/SNorm.java

.../oracle/truffle/r/test/engine/interop/AbstractMRTest.java

.../oracle/truffle/r/test/library/fastr/TestJavaInterop.java