* 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/libmain/shared.hh

@@ -3,6 +3,8 @@
 
 #include "types.hh"
 
+#include <signal.h>
+
 
 /* These are not implemented here, but must be implemented by a
    program linking against libmain. */
@@ -27,6 +29,10 @@ void printGCWarning();
 /* Whether we're running setuid. */
 extern bool setuidMode;
 
+extern volatile ::sig_atomic_t blockInt;
+
+MakeError(UsageError, nix::Error)
+
 }