Rf_eval implemented as a node + evaluates promises in pair-lists

...oracle/truffle/r/ffi/impl/common/JavaUpCallsRFFIImpl.java

...l/src/com/oracle/truffle/r/ffi/impl/nodes/RfEvalNode.java

...com/oracle/truffle/r/ffi/impl/upcalls/StdUpCallsRFFI.java

.../src/com/oracle/truffle/r/ffi/processor/FFIProcessor.java

...fle.r.test.native/packages/testrffi/testrffi/R/testrffi.R

...uffle.r.test.native/packages/testrffi/testrffi/src/init.c

...e.r.test.native/packages/testrffi/testrffi/src/testrffi.c

...e.r.test.native/packages/testrffi/testrffi/src/testrffi.h

...est.native/packages/testrffi/testrffi/tests/simpleTests.R