Add an option to enable/disable trace following of spawned childs or images

I'm thinking of adding an option to the function tracer, in order to enable or disable the tracing of "child" objects, like all the dynamical libraries invoked and loaded during the execution of the main program.

This would help with coverage of e.g. graphical applications, since we might want to test software like `Firefox` or `Kate` but we don't want to get coverage data for the whole wayland/gtk/qt environment.

Most likely we need to add a command line switch to the `FuncTracer.so` library; the same option must be reflected in the `wrap` process, to propagate it at the `pin` execution level.

Design proposals are welcome. What should be the default ? Should we have a "deep" wrap and a "shallow" one ? Should we rely on an environment variable, or a configuration file ?

Start by reading the FuncTracer.so command-line handling and the wrap process, then follow how options are propagated to pin execution. Compare the tracing behavior for spawned child objects and dynamically loaded libraries. Done means an agreed configuration design is implemented consistently across these entry points and verified for both enabled and disabled child or image tracing.

Written by the indexing model from the issue text.