* Change channel data structure. Now, instead of being tagged with a

* Change channel data structure.  Now, instead of being tagged with a
  "type", it is tagged with a "class".  The "class" has associated
  operations, so that basic channel operations such as reading and
  writing are generic.  This change allows the code to be modularized
  a bit better, and will facilitate the introduction of sockets.

* Eliminate the procedure NT_pipe_channel_available, replacing it with
  the generic procedure NT_channel_n_read.

* Eliminate references to long-obsolete "console" stuff.

* Change file-pointer positioning code to use SetFilePointer rather
  than __llseek.

* Don't try to signal an error if MsgWaitForMultipleObjects returns an
  unexpected answer -- only if it returns WAIT_FAILED.  We are only
  using it as a mechanism for blocking.

* Make cosmetic changes, eliminating unnecessary instances of "DEFUN"
  and the like.  These were introduced for unix, because there were
  non-ANSI compilers at that time.  On NT, all compilers are ANSI.