rffi: DLL class refactored to use Nodes

...m/oracle/truffle/r/engine/interop/ffi/TruffleCAccess.java

...c/com/oracle/truffle/r/engine/interop/ffi/TruffleDLL.java

...com/oracle/truffle/r/engine/interop/ffi/TruffleStats.java

.../src/com/oracle/truffle/r/library/graphics/RGraphics.java

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

.../nodes/builtin/base/foreign/CallAndExternalFunctions.java

...le/r/nodes/builtin/base/foreign/FortranAndCFunctions.java

...om/oracle/truffle/r/runtime/ffi/generic/Generic_Grid.java

...m/oracle/truffle/r/runtime/ffi/generic/Generic_Tools.java

...fi/src/com/oracle/truffle/r/runtime/ffi/jni/JNI_Call.java

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

...i/src/com/oracle/truffle/r/runtime/ffi/jni/JNI_Stats.java

...rc/com/oracle/truffle/r/runtime/ffi/CallRFFIRootNode.java

...e.r.runtime/src/com/oracle/truffle/r/runtime/ffi/DLL.java

...runtime/src/com/oracle/truffle/r/runtime/ffi/DLLRFFI.java

...me/src/com/oracle/truffle/r/runtime/rng/user/UserRNG.java