-c sequences=N suboptimal at N expression cutoff

N = 2:
  a;
  b;
  c;
  d;
was:
  a, b;
  c;
  d;
now:
  a, b;
  c, d;

fixes #1455
closes #1457

lib/compress.js

@@ -749,7 +749,10 @@ merge(Compressor.prototype, {
                 seq = [];
             };
             statements.forEach(function(stat){
-                if (stat instanceof AST_SimpleStatement && seqLength(seq) < compressor.sequences_limit) {
+                if (stat instanceof AST_SimpleStatement) {
+                    if (seqLength(seq) >= compressor.sequences_limit) {
+                        push_seq();
+                    }
                     seq.push(stat.body);
                 } else {
                     push_seq();