[GR-2527] TruffleNFI: prevent RNull converting to null; add remaining RFFI impls.

...m/oracle/truffle/r/engine/interop/CaptureNamesImplMR.java

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

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

...e/truffle/r/engine/interop/RForeignAccessFactoryImpl.java

...gine/src/com/oracle/truffle/r/engine/interop/RNullMR.java

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

...om/oracle/truffle/r/engine/interop/UnameUpCallImplMR.java

...cle/truffle/r/engine/interop/ffi/nfi/TruffleNFI_Base.java

...oracle/truffle/r/engine/interop/ffi/nfi/TruffleNFI_C.java

...cle/truffle/r/engine/interop/ffi/nfi/TruffleNFI_Call.java

...cle/truffle/r/engine/interop/ffi/nfi/TruffleNFI_Misc.java

...cle/truffle/r/engine/interop/ffi/nfi/TruffleNFI_PCRE.java

...e/truffle/r/engine/interop/ffi/nfi/TruffleNFI_REmbed.java

...ffle/r/engine/interop/ffi/nfi/TruffleNFI_RFFIFactory.java

...le/truffle/r/engine/interop/ffi/nfi/TruffleNFI_Tools.java

....truffle.r.native/fficall/src/truffle_nfi/call_rffi.c.not

...acle.truffle.r.native/fficall/src/truffle_nfi/misc_rffi.c