added some comments

src/policy.cpp

@@ -817,6 +817,9 @@ namespace libtorrent
 		return true;
 	}
 
+	// it's important that we don't dereference
+	// p here, since it is allowed to be a dangling
+	// pointer. see smart_ban.cpp
 	bool policy::has_peer(policy::peer const* p) const
 	{
 		// find p in m_peers

src/smart_ban.cpp

@@ -196,6 +196,10 @@ namespace libtorrent { namespace
 					// from the first time it sent it
 					// at least one of them must be bad
 
+					// verify that this is not a dangling pointer
+					// if the pointer is in the policy's list, it
+					// still live, if it's not, it has been removed
+					// and we can't use this pointer
 					if (!m_torrent.get_policy().has_peer(p)) return;
 
 #ifdef TORRENT_LOGGING