[Gdb] Printing complex types

[Peter Fraser]

When I write a large program. I always write a routines
to printout the values of various types. Quite often
these routines also carry out consistence checks
on values within these types.  Since GDB is one
of the very few debugger that allows the user
to call routines out of the debugged code, I can
use "p dump_value(value)" .  I make (as I expect
the rest of the world does also)  errors and pick
the wrong "dump" routine for the variable that I
want to look at. This often leads to unwanted
faults.  It would be very useful to be able to 
associate with a type a format or a routine to call
to print the value a variable.