* Changes to the command line syntax of Nix.

* A function to find all Nix expressions whose output ids are
  completely contained in some set.  Useful for uploading relevant Nix
  expressions to a shared cache.

src/store.cc

@@ -148,6 +148,15 @@ void unregisterPath(const string & _path)
 }
 
 
+bool queryPathId(const string & path, FSId & id)
+{
+    string s;
+    if (!queryDB(nixDB, dbPath2Id, path, s)) return false;
+    id = parseHash(s);
+    return true;
+}
+
+
 bool isInPrefix(const string & path, const string & _prefix)
 {
     string prefix = canonPath(_prefix + "/");