Merge branch 'grubba/pty-handling' into 8.0

* grubba/pty-handling: (23 commits)
  I/O [NT]: Fixed typo in FD_DEBUG code.
  I/O [NT]: Updated note.
  I/O [NT]: Added some notes about pty handling.
  I/O [NT]: More pty handling fixes.
  I/O [NT]: Keep track of processes using ConPTY slaves.
  I/O [NT]: Do not attempt to read too much data from ptys.
  I/O [NT]: Changed calling convention for close_pty().
  I/O [NT]: debug_fd_openpty() now returns ENOTSUPP when no ConPTY.
  I/O [NT]: Fixed some issues with debug_fd_openpty().
  Process [NT]: Fix process creation.
  I/O [NT]: More debug_fd_openpty() fixes:
  I/O [NT]: Fixed multiple isses with debug_fd_openpty().
  I/O [NT]: Adjusted preprocessor conditionals.
  I/O [NT]: Fixed typo.
  I/O [NT]: Fixed some issues with debug_fd_openpty().
  Process [NT]: Fixed some typos in recent commits.
  Process.create_process [NT]: First go at attempting to support ptys.
  I/O [NT]: Make Pike_NT_* available to the rest of Pike.
  Process[NT]: Switch to using STARTUPINFOEXW.
  I/O [NT]: Added debug_fd_openpty().
  ...