found /usr/local/bin/flex, we'll use this. Use --with-flex to specify another.
checking flex version... configure: WARNING: Flex version 2.6.4 found.
 Version 2.5.31 or greater is required. You can generally ignore this
 warning unless you need to regenerate psp_parser.c from psp_parse.l.
 If you do need regenerate psp_parser.c, use --with-flex to specify the
 location of the correct flex version. See the README for more information.