First, determine if your OS supports the full 28 functions of the
POSIX.1e draft (if so, LEVEL2) or only the first 11 functions (most
common case, meaning LEVEL1).

If your OS supports only LEVEL1, modift setup.py as appropriately;
unfortunately, the functionality of the module is quite low.

If your OS supports LEVEL2, there is a function which you must define:
testing if an acl_permset_t contains a given permission. For example,
under Linux, the acl library defines:
    int acl_get_perm(acl_permset_t permset_d, acl_perm_t perm);
under FreeBSD, the acl_permset_t is actually a mode_t and you can test
with |. So just see how this is implemented in your platform and
define a function:
    static int get_perm(acl_permset_t permset_d, acl_perm_t perm);
which return 1 if the permset contains perm and 0 otherwise. Put that
function in a separate file, os_<your os>.c and modify the top of
acl.c to include that file (see there for example).