maint: unload luaposix > v32 correctly.
maint: unload luaposix > v32 correctly.

* lib/specl/util.lua: Unload any module with a name prefixed by
"posix", in order that autoloaded submodules for an installed
recent luaposix are dropped in favour of test versions as
necessary.

Signed-off-by: Gary V. Vaughan <f9023000f29773649f3850298becb9544b5fd6a9@gnu.org>

gvvaughan/specl