Fix a long-standing bug: if this package is installed on NetBSD with
readline emulation, the GNU readline library which this module depends
on would not be picked up, causing "perl -d -e '1;'" to fail to start
the perl debugger because it could not find the rl_initialize function.
Instead, point includes and libs into ${PREFIX}, so that we have a chance
of picking up the proper GNU readline library.

(he)