Adds comments dag_node.
Replaces # SYMBOL with task categories.
Added support for password authentication between master and worker.
Updated copyright boilerplate.
Combined all uses of srand into a common random_init().
Changed all isntances of srand to random_init().
Small fixes for work queue authentication.

- Added -P as an option to work_queue_worker to indicate the password
  file.
- Updated documentation to make clear the difference between the
  password file and the password itself.
- copy_file_to_buffer behaves like other functions in copy_stream.
Remove debugging fprintf from copy_file_to_buffer.