This change includes a minor change to semantics for
reinitialization().

There are three chief performance-related changes:

    - Do not check whether logging is enabled in the actual log call.
      Instead check enviroment variables when the module is imported
      and whenever an explicit initialize() call is made.

      This might seem like it limits the user's ability to turn
      logging on and off, but I don't believe it does.  Logging is
      controlled by environment variables.  Once the Python script is
      working, the environment variables won't change.

      This change makes the case of no logging fast, instead of slow.

    - Each log call goes through a method on the stupid_log_write()
      object instead of through __call__().  It's much faster to call
      a method than an instance.

    - Use "print >> file" rather than "file.write()".  It appears to
      be a bit faster.

Replaced _set_stupid_dest() with _set_log_dest().