fixed checks for readline (HAVE_READLINE -> HAVE_LIBREADLINE)

config.h provides HAVE_LIBREADLINE, but there were two places in the code that used HAVE_READLINE instead.

In interactiveTests/scuff-test-PPIs.cc, config.h is not included in fact, but HAVE_READLINE defined and used directly. I changed it to HAVE_LIBREADLINE for consistency, but otherwise left as is.