112.01.00

- Changed `Writer.transfer write pipe` to close `pipe` when the
  `writer`, is closed.

  Previously, `Writer.transfer` did not close the pipe when the
  underlying writer is closed.  This was strange because:

  1. Callers would have to consistently check for the writer being
     closed and close the `Pipe.Reader`t= themselves
  2. The analogous function `Pipe.transfer` closes the reader on
     similar circumstances.

  The absence of the close was noticed as a bug in `Rpc`, which
  assumed that `Writer.transfer` did the close.
- Fixed a bug in `Scheduler.yield` that caused it to pause for 50ms if
  there is no other pending work and no I/O.
- Exposed type equivalence between `Unix.Passwd.t` and
  `Core.Std.Unix.Passwd.t`.
- Changed `Writer.write_bin_prot` to use the new
  `Bigstring.write_bin_prot`.