Fix coding styles in test/benchmarks.js.

https://code.google.com/p/esprima/issues/detail?id=529
Remove duplicate markEnd

https://code.google.com/p/esprima/issues/detail?id=528
Accurate node creation.

Issue 530: Reducing memorizing start position by create nodes at the
right location as much as possible.
Minimized the number of skipComment calls