"testthat" has been tested running tests of package "argparse".

- implemented RFFI functions PRSEEN, PRENV, R_PromiseExpr, and PRCODE
- cleanup of method "getIntrinsicValue"; replaced by RASTUtils.createLanguageElement
- added dummy cast to node IsATTY
- also fixed FileConnections.writeString; was required to run a package
- added tests for R exception handling; since we still have bugs, some tests are ignored
- also fixed a problem during source code parsing in REngine, which occurred if the code contained empty lines that have not been suppressed by any shell

rffi; replace UpCallsIndex with RFFIUpCallMethod enum; fix bug in R_NewHashedEnv signature; simplify RForeignAccessFactoryImpl

RFFI: refactor upcalls into separate interfaces; fix R_Home/R_Interactive rewrites; make tempdir context sensitive, clean up CallRFFI

rffi: C, Call, Grid, Lapack, PCRE, RAppl, STats, Tools, UserRNG as Truffle Node; refactor ForeignFunctions to keep C/Fortran together

rffi: add interface for RFFI upcalls; refactor native layer to use instance not static class; add factory for alternate upcall implementations

refactor TestRFFIPackage, add more tests; (pessimally) fix “complete” status of vectors updated in RFFI