[PATCH]: add set/show debug, move gdb debugging flags into it

[Eli Zaretskii]

> > I always consider it questionable whether maintenance commands
> > SHOULD be documented in the user's guide.  If they should,
> > perhaps it should be in a separate section clearly identified
> > as being for the maintenance and debugging of the debugger.
> 
> I agree (I prefer the second option -- a separate section).  That is why
> I said it was a policy issue.

Separate section is fine.  My point was that they should be
*somewhere* in the manual, and they should have an index entry.