Make 'Go' hierarchy independent of relabelling.

Make 'Go' hierarchy independent of relabelling.

This allows to move 'Go' initialization loop to 'DFA::prepare'
and thus avoid ugly check if it is already initialized (it can
happen in '-r' mode when the same DFA is used multiple times).
Now that we store 'State *' pointers instead of labels in
'CpgotoTable', relabelling won't affect the generated code.