[io] Release Pipe and Console shared handles

[io] Release Pipe and Console shared handles

Allows opening a character device or named fifo more than once with code like:

  using (var f = new FileStream ("/dev/zero", FileMode.Open))
  {
    ...
  }
  using (var f = new FileStream ("/dev/zero", FileMode.Open))
  {
    ...
  }