```catch``` generate new variable.

Created by: tuchida

New hygiene is very cool. But I found a small problem.

input:

var r;
var e = 'not error';

macro main {
  case ($a) => {
    try {
      a();
    } catch(e) {
      sub($a);
    }
  }
}

macro sub {
  case ($b) => {
    r = e
  }
}

main(1);
console.log(r === e);

output:

var r$3;
var e$4 = 'not error';
try {
    a();
} catch (e$4) {
    r$3 = e$4;
}
;
console.log(r$3 === e$4);

I expected catch (e$5) and print true by console.log.