fix: gcc4.2 / PPC compilation

no match for 'operator!=' in 'x != std::list<_Tp, _Alloc>::rend()
[with _Tp = long long int, _Alloc = std::allocator<long long int>]()'

libs/ardour/playlist.cc

@@ -1959,7 +1959,7 @@ Playlist::find_next_transient (framepos_t from, int dir)
 			}
 		}
 	} else {
-		for (AnalysisFeatureList::const_reverse_iterator x = points.rbegin(); x != points.rend(); ++x) {
+		for (AnalysisFeatureList::reverse_iterator x = points.rbegin(); x != points.rend(); ++x) {
 			if ((*x) <= from) {
 				reached = true;
 			}