Don't copy <*> regexps for each condition.

Don't copy <*> regexps for each condition.

There're two major things to care about in this situation:
1. <*> rules must have the lowest priority: in order to guarantee
   it, we re-iterate <*> regexps after all other rules have been
   parsed and fix <*> regexps priority.
2. <*> regexps must be compiled to instrictions separately for each
   condition: this is guaranteed by assigning them
   're2c::RegExp::PRIVATE' attribute.

Note that 're2c::RuleOp::accept' member stores rule priority.
These priorities don't have to be consecutive, only the right order
must be maintained. Later on in 're2c::DFA::prepare' they result in
consecutive 'yyaccept' values.