A tentative patch to fix compilation with R 3.0
fix for #2 (some cleanup)
fix for #2 (now it compiles)
bugfix: the interpreter should be set to non interactive

otherwise the interpreter may prompt the user and hang the execution
inappropriately.
bugfix: undo non-interactive mode

setting the embedded interpreter to non-interactive has one major
consequence: signaling errors via [error] halts execution in a way
that seems not compatible with [R_tryError]