Use MAX* cosistently

pkg used MAXPATHLEN, MAXLOGNAME and PATH_MAX inconsistently,
sometimes path[MAXPATHLEN] and sometimes path[MAXPATHLEN + 1].

Since those constants already include the trailing '\0' and snprintf's
size parameter also does, it was changed to path[MAXPATHLEN] (or
MAXLOGNAME, PATH_MAX) everywhere.
Merge branch 'master' of git://github.com/grembo/pkg into grembo-master