rename_to() and copy_to() are heavy operations and should be BLOCKING

dtool/src/dtoolutil/filename.h

@@ -213,8 +213,8 @@ PUBLISHED:
   bool chdir() const;
   bool touch() const;
   bool unlink() const;
-  bool rename_to(const Filename &other) const;
-  bool copy_to(const Filename &other) const;
+  BLOCKING bool rename_to(const Filename &other) const;
+  BLOCKING bool copy_to(const Filename &other) const;
 
   bool make_dir() const;
   bool mkdir() const;