Mark some modules as skip-over-when-stepping in

[matthewpersico]

Much like you can tell some modules that they should not be the location of a Carp (see CARP_NOT), we should be able to have a STEPINTO_NOT configured with particular modules or particular behavior, such as when you are stepping into a function that has funciton calls in the arguments, you probably don't want to step into the args' function calls.

Or perhaps we add a 'shallow-step' command that will skip stepping into function arg function calls.