Up to now, a state had a set of follow-on positions. It is replaced a
set of current positions. This change will save memory space.
dfa.c (leaf_set): Remove it.
(struct dfa): Add new member constraints and separates.
(append): New function.
(state_index): Bring constraint from pre-calculated.
(state_separate_contexts): Bring separate contexts from pre-calculated.
Change argument, update callers.
(merge_nfa_state): Pre-calculate constraints for END. and remove END.
No longer END is not used after here.
(dfaoptimize): Initialize added member constraints.
(dfaanalyze): Pre-calculate seprate contexts.
(build_state): Change for this update.
(dfassbuild): Initialize new members .
(dfafree): Free memory for new members.