Restructured determinization algorithm DFA construction in a more canonical way.

Restructured determinization algorithm DFA construction in a more canonical way.

All textbooks describe determinization (powerset construction)
like this:

    S0 <- epsilon-closure of start NFA state
    add S0 to DFA
    while there is unmarked state S:
        mark S
        for each symbol X in the alphabet:
            R <- the set of NFA states reachable from S on X
            T <- epsilon-closure of R
            if T is not in DFA
                add T to DFA

In re2c the inner loop on alphabet symbols was split in two parts
and somewhat obfuscated; this commit makes re2c follow textbook
version more closely.