Fix line numbers in JavaScript stack traces

Instead of calling the function constructor to compile script in Sky, we now
concatenate strings. This has the advantage of making the line numbers
generated in error messages correct but the disadvantage of being a hack. I've
filed https://code.google.com/p/v8/issues/detail?id=3624 to request a proper
API for this purpose.

R=esprehn@chromium.org

Review URL: https://codereview.chromium.org/688033003