[GR-2738] Fix various warnings.

...fle.r.engine/src/com/oracle/truffle/r/engine/REngine.java

...com/oracle/truffle/r/engine/interop/RInteropScalarMR.java

...tin/src/com/oracle/truffle/r/nodes/builtin/base/Attr.java

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

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

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

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

...c/com/oracle/truffle/r/nodes/builtin/base/UpdateAttr.java

.../com/oracle/truffle/r/nodes/builtin/fastr/FastrDqrls.java

...acle/truffle/r/nodes/access/vector/ExtractVectorNode.java

...m/oracle/truffle/r/nodes/function/ClassHierarchyNode.java

...src/com/oracle/truffle/r/nodes/unary/CastLogicalNode.java

...src/com/oracle/truffle/r/runtime/ffi/jni/JNI_PkgInit.java

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

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

...le.r.runtime/src/com/oracle/truffle/r/runtime/RError.java

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

...oracle/truffle/r/runtime/builtins/RBuiltinDescriptor.java

...rc/com/oracle/truffle/r/runtime/nmath/GammaFunctions.java

...runtime/src/com/oracle/truffle/r/runtime/nmath/RMath.java