Fix assert for who_points_at monitor cmd for an interiorly pointed block

* fix the assert
* some better comments
* update test to verify who_points_at behaviour with an interiorly pointed block



git-svn-id: svn://svn.valgrind.org/valgrind/trunk@13609 a5019735-40e9-0310-863c-91ae7b9d1cf9
diff --git a/memcheck/mc_include.h b/memcheck/mc_include.h
index 728e7b8..46e824d 100644
--- a/memcheck/mc_include.h
+++ b/memcheck/mc_include.h
@@ -513,7 +513,7 @@
   }
   LeakCheckHeuristic;
 
-// Nr of heuristics.
+// Nr of heuristics, including the LchNone heuristic.
 #define N_LEAK_CHECK_HEURISTICS 4
 
 // Build mask to check or set Heuristic h membership