try harder to keep root cause of exceptions, make NFI upcalls interface public

...oracle/truffle/r/engine/shell/EmbeddedConsoleHandler.java

...gine/src/com/oracle/truffle/r/engine/shell/REmbedded.java

...com/oracle/truffle/r/ffi/impl/nfi/TruffleNFI_PkgInit.java

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

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

...fle.r.runtime/src/com/oracle/truffle/r/runtime/Utils.java

...me/src/com/oracle/truffle/r/runtime/env/REnvironment.java

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