prolog:debug_control_hook(:Action)Hook for the debugger control predicates that allows the creator of more 
high-level programming languages to use the common front-end predicates 
to control the debugger. For example, XPCE uses these hooks to allow for 
spying methods rather than predicates. Action is one of:
- spy(Spec)
- Hook in spy/1. 
If the hook succeeds spy/1 
takes no further action.
- nospy(Spec)
- Hook in nospy/1. 
If the hook succeeds nospy/1 
takes no further action. If spy/1 
is hooked, it is advised to place a complementary hook for
nospy/1.
- nospyall
- Hook in nospyall/0. 
Should remove all spy points. This hook is called in a failure-driven 
loop.
- debugging
- Hook in debugging/0. 
It can be used in two ways. It can report the status of the additional 
debug points controlled by the above hooks and fail to let the system 
report the others, or it succeeds, overruling the entire behaviour of debugging/0.
[multifile]prolog:debug_control_hook(+Action)Allow user-hooks in the Prolog debugger interaction. See the calls below 
for the provided hooks. We use a single predicate with action argument 
to avoid an uncontrolled poliferation of hooks.