Replace most uses of std::cerr with util::dprint

luprex/cpp/core/world-diffxmit.cpp

@@ -1,4 +1,3 @@
-#include <iostream>
 
 #include "world.hpp"
 
@@ -294,9 +293,7 @@ void World::patch_source(StreamBuffer *sb, DebugCollector *dbc) {
     if (modified) {
         eng::string errs = source_db_.rebuild();
         DebugLine(dbc) << "Source DB rebuilt";
-        // TODO: I don't currently have any good place to send the
-        // error messages.  This is a stopgap.
-        std::cerr << errs;
+        util::dprint(errs);
     }
 }