DATAPTR supports complex, charsxp and shows informative error for character vectors

...e.truffle.r.native/fficall/src/common/Rinternals_common.c

...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