support reading from commands by adppending | to the filename.
support streaming reads from command.
Fix something to make rearead work better. (magically happened)
Note that fdstream.h is from boost and has a separate license:
* (C) Copyright Nicolai M. Josuttis 2001.
* Permission to copy, use, modify, sell and distribute this software
* is granted provided this copyright notice appears in all copies.
* This software is provided "as is" without express or implied
* warranty, and with no claim as to its suitability for any purpose.