Tell player if monster can never be recited to (m-aigner / 10416)

This adapts m-aigner's code from #379

The previous messaging seemed to have been actively wrong (the HD
calculation is different than what seems to happen in god-abil.cc), so I
decided it was time to finally merge a version of this, fixing the crash
discussed in the PR thread. The new version still only checks particular
monsters, so as discussed in the PR thread, something that looks at a
monster_info might be desireable. In principle this more accurate info
can leak information about a monster's spellset, but for that to happen,
I think there would have to be something like a monster with multiple
spellsets and subhuman intelligence, which as far as I can tell doesn't
exist right now.  Calculating over monster_info might deal with that
case as well, if it were to ever come about.

Resolves #379

crawl-ref/source/describe.cc

@@ -3733,23 +3733,22 @@ static string _monster_stat_description(const monster_info& mi)
     if (mon_size)
         result << uppercase_first(pronoun) << " is " << mon_size << ".\n";
 
-    if (in_good_standing(GOD_ZIN, 0))
-    {
-        const int check = mi.hd - zin_recite_power();
-        if (check >= 0)
-        {
-            result << uppercase_first(pronoun) << " is too strong to be"
-                                                  " recited to.";
-        }
-        else if (check >= -5)
+    if (in_good_standing(GOD_ZIN, 0) && !mi.pos.origin() && monster_at(mi.pos))
+    {
+        recite_counts retval;
+        monster *m = monster_at(mi.pos);
+        auto eligibility = zin_check_recite_to_single_monster(m, retval);
+        if (eligibility == RE_INELIGIBLE)
+            result << "Reciting Zin's laws will not affect " << pronoun << ".";
+        else if (eligibility == RE_TOO_STRONG)
         {
-            result << uppercase_first(pronoun) << " may be too strong to be"
-                                                  " recited to.";
+            result << uppercase_first(pronoun) <<
+                    " is too strong to be affected by reciting Zin's laws.";
         }
-        else
+        else // RE_ELIGIBLE || RE_RECITE_TIMER
         {
-            result << uppercase_first(pronoun) << " is weak enough to be"
-                                                  " recited to.";
+            result << uppercase_first(pronoun) <<
+                            " can be affected by reciting Zin's laws to it.";
         }
 
         if (you.wizard)

crawl-ref/source/god-abil.cc

@@ -620,7 +620,7 @@ static int _heretic_recite_weakness(const monster *mon)
         && !(mon->has_ench(ENCH_DUMB) || mons_is_confused(*mon)))
     {
         // In the eyes of Zin, everyone is a sinner until proven otherwise!
-            degree++;
+        degree++;
 
         // Any priest is a heretic...
         if (mon->is_priest())