Add a time+layer equivalence check

This is more useful than exact_equivalent() since _start offset
may not match in some cases (compounds, import, record with different
capture latencies).

However shared group editing (range, copy/paste) does result in
consistent layers and matching position+length.

libs/ardour/ardour/region.h

@@ -205,6 +205,7 @@ public:
 	bool size_equivalent (boost::shared_ptr<const Region>) const;
 	bool overlap_equivalent (boost::shared_ptr<const Region>) const;
 	bool enclosed_equivalent (boost::shared_ptr<const Region>) const;
+	bool layer_and_time_equivalent (boost::shared_ptr<const Region>) const;
 	bool region_list_equivalent (boost::shared_ptr<const Region>) const;
 	bool source_equivalent (boost::shared_ptr<const Region>) const;
 	bool any_source_equivalent (boost::shared_ptr<const Region>) const;

libs/ardour/ardour/types.h

@@ -631,7 +631,8 @@ typedef std::vector<boost::shared_ptr<Bundle> > BundleList;
 enum RegionEquivalence {
 	Exact,
 	Enclosed,
-	Overlap
+	Overlap,
+	LayerTime
 };
 
 enum WaveformScale {

libs/ardour/enums.cc

@@ -694,6 +694,7 @@ setup_enum_writer ()
 	REGISTER_ENUM(Exact);
 	REGISTER_ENUM(Enclosed);
 	REGISTER_ENUM(Overlap);
+	REGISTER_ENUM(LayerTime);
 	REGISTER(_RegionEquivalence);
 
 	REGISTER_ENUM(Linear);

libs/ardour/playlist.cc

@@ -846,6 +846,13 @@ Playlist::get_equivalent_regions (boost::shared_ptr<Region> other, vector<boost:
 				 }
 			 }
 			 break;
+		 case LayerTime:
+			 for (RegionList::iterator i = regions.begin(); i != regions.end(); ++i) {
+				 if ((*i)->layer_and_time_equivalent (other)) {
+					 results.push_back (*i);
+				 }
+			 }
+			 break;
 		 case Enclosed:
 			 for (RegionList::iterator i = regions.begin(); i != regions.end(); ++i) {
 				 if ((*i)->enclosed_equivalent (other)) {

libs/ardour/region.cc

@@ -1484,6 +1484,14 @@ Region::enclosed_equivalent (boost::shared_ptr<const Region> other) const
 	       (first_sample() <= other->first_sample() && last_sample() >= other->last_sample()) ;
 }
 
+bool
+Region::layer_and_time_equivalent (boost::shared_ptr<const Region> other) const
+{
+	return _layer == other->_layer &&
+		_position == other->_position &&
+		_length == other->_length;
+}
+
 bool
 Region::exact_equivalent (boost::shared_ptr<const Region> other) const
 {