Description: A task dependency manager for async things in node.js.

Usage: Create a new AsyncDependencyObject with a hash of tasks, 
       where the keys are the task names and the function names 
       are underscore-separated names of the prerequisite task names.
       
       In your functions, assign this as the callback function to your async 
       operation. this is assigned to an internal task management callback 
       that will call more tasks.
       
       When your dependent tasks get called, the first argument will be an 
       object where the keys are the prerequisite task names and the values 
       are the arguments that were provided to the internal task management 
       callbacks.

Usage Example:
new AsyncDependencyManager(
  {
    a: function () {
      sys.puts('a');
      setTimeout(this,Math.random()*1000);
    },
    b: function () {
      sys.puts('b');
      setTimeout(this,Math.random()*1000);
    },
    c: function a_b() {
      sys.puts('c');
      setTimeout(this,Math.random()*1000);
    },
    d: function c() {
      sys.puts('d');
      setTimeout(this,Math.random()*1000);
    },
    e: function c() {
      sys.puts('e');
      setTimeout(this,Math.random()*1000);
    },
    f: function d_c() {
      sys.puts('f');
      setTimeout(this,Math.random()*1000);
    },
    g: function e() {
      sys.puts('g');
      setTimeout(this,Math.random()*1000);
    },
    h: function f() {
      sys.puts('h');
      setTimeout(this,Math.random()*1000);
    },
    i: function g() {
      sys.puts('i');
      setTimeout(this,Math.random()*1000);
    },
    j: function f_g() {
      sys.puts('j');
      setTimeout(this,Math.random()*1000);
    }
  });