* Daemon mode (`nix-worker --daemon'). Clients connect to the server

via the Unix domain socket in /nix/var/nix/daemon.socket.  The
  server forks a worker process per connection.
* readString(): use the heap, not the stack.
* Some protocol fixes.

src/libutil/types.hh

@@ -44,8 +44,6 @@ public:
         newClass(const format & f) : superClass(f) { }; \
     };
 
-MakeError(UsageError, Error)
-
 
 typedef list<string> Strings;
 typedef set<string> StringSet;