• ~.PopenSpawn now has a preexec_fn parameter, like ~.spawn and subprocess.Popen, for a function to be called in the child process before executing the new command. Like in Popen, this works only in POSIX, and can cause issues if your application also uses threads.
• Significant performance improvements when processing large amounts of data.
• Ensure that spawn.closed gets set by ~.spawn.close, and improve an example for passing SIGWINCH through to a child process.

Tested with python-ipython and python3-ipython.