Prevent identical port-names when renaming tracks

Audio ports are sorted using PBD::naturally_less.
PBD::naturally_less is also used as compare function
for port-lists, port-sets, and port-maps.

So in sets and maps, the function is used to test
for uniqueness. This lead to issues since naturally_less
treats whitespace and underscores as identical.

While it was possible to have routes named "Audio_1",
and "Audio 1", this resulted in missing ports for one
of the routes.

see also 60ff3ef764

libs/ardour/route.cc

@@ -4810,9 +4810,8 @@ Route::has_io_processor_named (const string& name)
 	ProcessorList::iterator i;
 
 	for (i = _processors.begin(); i != _processors.end(); ++i) {
-		if (boost::dynamic_pointer_cast<Send> (*i) ||
-		    boost::dynamic_pointer_cast<PortInsert> (*i)) {
-			if ((*i)->name() == name) {
+		if (boost::dynamic_pointer_cast<IOProcessor> (*i)) {
+			if (0 == PBD::natcmp ((*i)->name().c_str(), name.c_str())) {
 				return true;
 			}
 		}