Schema that contain the equivalent of (a*)* (as in trac/172) are non-deterministic, and the number of pending unresolved automaton configurations will grow exponentially until a symbol match eliminates some of them. Impose a configurable limit on the amount of non-determinism, and allow the user to control whether exceeding that limit produces an error or simply resolves it arbitrarily.
fix #5: SF/173: place a limit on non-deterministic expansion
This is just a safety-check. With well-designed schema resolution
should never be non-deterministic; in practice, the test suite passes
with this set to 4, but for the real-world we'll increase the limit.