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/insight.c

@@ -1922,6 +1922,20 @@ attributes_enlightenment(
     }
 #endif
 
+    {
+        static const char *verbchoices[2][2] = {
+            { "might avoid", "have avoided" },
+            { "could have avoided", "avoided" },
+        };
+        /* u.usaving_grace will always be 0 or 1; final is 0 (game in
+           progress), 1 (game over, survived), or 2 (game over, died) */
+        const char *verb = verbchoices[!!final][u.usaving_grace];
+
+        /* 'verb' has already been set for present or past but enl_msg()
+           needs it twice, one for in progress, the other for game over */
+        enl_msg(You_, verb, verb, " a one-shot death via saving-grace", "");
+    }
+
     {
         const char *p;