libtool makes unreliable executable names

[philshafer]

libtool makes executable names that are not reliable, causing "make test" to fail with issues like:

https://reviews.freebsd.org/D20188

The fix is to use xo_program() with the basename of argv[0] to ensure consistent output.

Thanks,
Phil

[philshafer]

xo_parse_args has been altered to notice the ".test" extention and remove it from binary names.

Thanks,
Phil