[GR-2798] Fixes to enable testthat 2.

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

.../com/oracle/truffle/r/ffi/impl/nodes/ListAccessNodes.java

...acle/truffle/r/nodes/builtin/base/DatePOSIXFunctions.java

...com/oracle/truffle/r/nodes/builtin/base/EnvFunctions.java

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

...e/src/com/oracle/truffle/r/runtime/data/RDataFactory.java

...ntime/src/com/oracle/truffle/r/runtime/data/RPromise.java

...untime/src/com/oracle/truffle/r/runtime/data/RSymbol.java

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

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

...est/src/com/oracle/truffle/r/test/ExpectedTestOutput.test

...oracle/truffle/r/test/builtins/TestBuiltin_asPOSIXlt.java