Fix memory leaks in failure paths in buildACLCommands and parseAclItem.

Fix memory leaks in failure paths in buildACLCommands and parseAclItem.

This is currently only cosmetic, since all the call sites just curl up
and die in event of a failure return.  It might be important for some
future use-case, though, and in any case it quiets warnings from the
clang static analyzer (as reported by Anna Zaks).

Josh Kupershmidt