Integrate the tests from libxo into the FreeBSD test suite

The functional_test.sh harness for each test subdir was inspired
by the version in bin/sh/tests/functional_test.sh

Some gymnastics were required to deal with implicit rules for
.c / .o -> .out as the suffix transformation rules were
incorrectly trying to create the test outputs from some of the
source files

Sponsored by: EMC / Isilon Storage Division