additional tests for ffi and stats

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

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

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

...ruffle.r.test/src/com/oracle/truffle/r/test/TestBase.java

...com/oracle/truffle/r/test/builtins/TestBuiltin_solve.java

...m/oracle/truffle/r/test/generate/GnuROneShotRSession.java

...rc/com/oracle/truffle/r/test/library/stats/TestStats.java

...rc/com/oracle/truffle/r/test/library/utils/TestUtils.java

.../com/oracle/truffle/r/test/rpackages/TestRFFIPackage.java