Implementing sid at instrumentation time

[eliottrobson]

In the current implementation of sids, script ids, these are generated at runtime however because of this there is a bug.

If there are two scripts, script1.js and script2.js, any sid information about any hooks in script1 are lost as soon as script2 is loaded. This change implements the script id at instrumentation time and adds an extra sid parameter to all hooks.

The script enter hook can be used to catch the id and all future calls to any hook within that script will all exhibit the same sid allowing across file tracking. To implement a custom sid it's possible to pass an "thisSid" option to the instrumentCode method.