Add statement tracing

[ariya]

Insert a simple tracer before executing every statement. This is similiar to the function entrance and function exit (still planned) tracing, but having it per statement.

[nuwanc]

Will this feature enable the user to get a execution trace of a function?, like variable values at the time of running a function?

[ariya]

Just read http://ariya.ofilabs.com/2012/02/tracking-javascript-execution-during-startup.html for some background.