Merge pull request #301 in G/fastr from...

Merge pull request #301 in G/fastr from ~ADAM.WELC_ORACLE.COM/fastr:feature/rstudio_integration to master

* commit '68ae6160':
  Browser context is now simulated.
  Added support for comparing SEXP-s and contexts from native side.
  Added preliminary support for keeping context objects across native calls.
  Simulating browser context.
  Missing modifications for copying back Java objects on nested upcalls.
  Copying back Java object on nested upcalls.
  Fixed a call to tracing macro.
  Changed return type of a native interface API call so that we can preserve Java objects correctly on the native side.
  ffi: maintain stack of jmpbuf ptrs; run callEnter/callExit on Rembedded dowfalls
  FFI: implement R_Preserve/ReleaseObject and add test
  Another addition to the native API.
  While deparsing GNU R structures we need to expand attributes.