extending u.usaving_grace

Issue a livelog/#chronicle message if saving-grace saves the hero.
Right now it's classified as conduct for livelog filtering, because
I didn't want to implement a new category (needs update of global.h
and also the template 'sysconf') and conduct felt like the best fit
of the existing classifications.

Report whether saving-grace is available or already used, among
the attributes of magical enlightenment or end-of-game disclosure.

And move the fixes entry for it from the fixes section to the new
features section of fixes3-7-0.txt.

It seems likely that someone will want to turn not using saving-
grace into a tracked conduct.  That seems like overkill to me, not
to mention inflating the N for "N conduct games".

src/hack.c

@@ -4045,6 +4045,15 @@ saving_grace(int dmg)
     }
 
     if (!u.usaving_grace && dmg >= u.uhp && (u.uhp * 100 / u.uhpmax) > 90) {
+        /* saving_grace doesn't have it's own livelog classification;
+           we might invent one, or perhaps use LL_LIFESAVE, but surviving
+           certain death (or preserving worn amulet of life saving) via
+           saving-grace feels like breaking a conduct; not sure how best
+           to phrase this though... */
+        livelog_printf(LL_CONDUCT, "%s (%d damage, %d/%d HP)",
+                       "survived one-shot death via saving-grave",
+                       dmg, u.uhp, u.uhpmax);
+
         /* note: this could reduce dmg to 0 if u.uhpmax==1 */
         dmg = u.uhp - 1;
         u.usaving_grace = 1; /* used up */