for review: fix to mercury_trail.h comments

[Peter Schachte]

Fergus, could you please review this?  Thanks.

Estimated hours taken: .2

runtime/mercury_trail.h:
	Improved a few comments.

Index: runtime/mercury_trail.h
===================================================================
RCS file: /home/staff/zs/imp/mercury/runtime/mercury_trail.h,v
retrieving revision 1.5
diff -u -r1.5 mercury_trail.h
--- mercury_trail.h	1997/08/27 13:51:34	1.5
+++ mercury_trail.h	1997/08/28 00:56:26
@@ -43,6 +43,12 @@
 		save_ticket_counter = MR_ticket_counter;	\
 	} while(0)
 
+/* void MR_discard_ticket(void); */
+#define MR_discard_ticket()					\
+	do {							\
+		--MR_ticket_counter;				\
+	} while(0)
+
 /* void MR_discard_tickets_to(Word); */
 #define MR_discard_tickets_to(save_ticket_counter)		\
 	do {							\
@@ -64,7 +70,7 @@
 	  ** Unwind restoration info back to `old'.  `kind' indicates
 	  ** whether we are restoring or just discarding the info.
 	  */
-/* void MR_discard_tickets_to(Word, MR_trail_reason); */
+/* void MR_reset_ticket(Word, MR_untrail_reason); */
 #define MR_reset_ticket(old, kind)				\
 	do {							\
 		MR_TrailEntry *old_trail_ptr =  		\
@@ -76,12 +82,6 @@
 		}						\
 	} while(0)
 
-/* void MR_discard_tickets_to(void); */
-#define MR_discard_ticket()					\
-	do {							\
-		--MR_ticket_counter;				\
-	} while(0)
-
 /*---------------------------------------------------------------------------*/
 /*
 ** The following stuff defines the Mercury trail.
@@ -92,8 +92,8 @@
 /*---------------------------------------------------------------------------*/
 
 /*
-** MR_untrail_reason defines the possible reasons why a trail
-** entry may be activated and/or removed.
+** MR_untrail_reason defines the possible reasons why a function trail
+** entry may be activated (and then possibly removed).
 */
 typedef enum {
 	MR_undo,	/* ordinary backtracking on failure */
@@ -257,7 +257,7 @@
 /*---------------------------------------------------------------------------*/
 
 /*
-** void  MR_trail_value_at_address(Word *address, Word value);
+** void  MR_trail_value(Word *address, Word value);
 **
 ** Make sure that when the current execution is
 ** backtracked over, `value' is placed in `address'.