Exclude specific functions in PathTracer

[sema]

Build the infrastructure to express the identity of JavaScript functions, and use this to exclude certain functions from being handled in the PathTracer (or to flatten all calls made within a matched function).

Some JavaScript functions are anonymous functions bound to variables, and thus have no name. We could identify them from where they are bound (they can potentially be bound in multiple places).

We need to come up with some good strategy to identify the JavaScript functions, even the anonymous ones.