Allow Ru abilities under Silence.

Ru's abilities aren't invocations to the god, but rather ways you
can use the power you've gained through sacrifice, so you don't
need to be able to be heard in order to use them.

crawl-ref/source/ability.cc

@@ -1523,7 +1523,8 @@ static bool _check_ability_possible(const ability_def& abil,
         return false;
     }
 
-    if (silenced(you.pos()) && !you_worship(GOD_NEMELEX_XOBEH))
+    if (silenced(you.pos()) && !you_worship(GOD_NEMELEX_XOBEH)
+          && !you_worship(GOD_RU))
     {
         talent tal = get_talent(abil.ability, false);
         if (tal.is_invocation)
@@ -4043,7 +4044,9 @@ vector<ability_type> get_god_abilities(bool include_unusable, bool ignore_piety)
     // Remaining abilities are unusable if under penance, or if silenced if not
     // Nemelex abilities.
     if (!include_unusable && (player_under_penance()
-                              || silenced(you.pos()) && !you_worship(GOD_NEMELEX_XOBEH)))
+                              || silenced(you.pos())
+                              && !you_worship(GOD_NEMELEX_XOBEH)
+                              && !you_worship(GOD_RU)))
     {
         return abilities;
     }