Add support for exceptions to the debugger, and

Estimated hours taken: 8

Add support for exceptions to the debugger, and
add support for debugging to the exception module.

browser/debugger_interface.m:
	Add `exception' to the trace_port_type enumeration.

runtime/mercury_trace_base.h:
	Add MR_PORT_EXCEPTION to the MR_Trace_Port enumeration.

trace/mercury_trace_internal.c:
trace/mercury_trace.h:
trace/mercury_trace.c:
	Modify the code to handle MR_PORT_EXCEPTION.

extras/exceptions/exception.m:
	- Define stack layout structures for the hand-written procedures
	  `builtin_throw' and `builtin_catch'.
	- Use mktempframe() rather than mkframe() to allocate the temporary
	  frames used to prevent hijacking of the exception-catching frame
	  (this is more efficient, and avoids the need to give a stack
	  layout for those frames).
	- Change the code for builtin_throw/1 so that if MR_trace_enabled
	  is true, it calls a new function trace_throw(), which calls
	  MR_trace(..., MR_PORT_EXCEPTION, ...) for each stack frame.
	- Fix some type errors occurring for non-GC grades.
	- Fix some uses of obsolete names (e.g. replace `hp' with `MR_hp').

runtime/mercury_trace_base.c:
compiler/trace.m:
	Add some comments relating to the above changes.

browser/debugger_interface.m

@@ -56,6 +56,7 @@ dummy_pred_to_avoid_warning_about_nothing_exported.
 	;	switch
 	;	nondet_pragma_first
 	;	nondet_pragma_later
+	;	exception
 	.
 
 :- type goal_path_string == string.