Add pseudoterminal support to the unix package

[bos@…]

I propose to enhance the unix package by adding pty support:

-- | @openPseudoTerminal@ creates a pseudoterminal (pty) pair, and -- returns the newly created pair as a (@master@, @slave@) tuple. openPseudoTerminal :: IO (Fd, Fd)

-- | @getSlaveTerminalName@ calls @ptsname@ to obtain the name of the -- slave terminal associated with a pseudoterminal pair. The file -- descriptor to pass in must be that of the master. getSlaveTerminalName :: Fd -> IO FilePath?

This is all that's required to get pseudoterminals working on Unix-like systems.

[bos@…]

The code ought to work on Linux, Solaris, BSD, and HP/UX. Probably Cygwin, too. However, I've only been able to compile-test it on Linux.

[simonmar]

No objection in principle; the code does stuff I don't understand so I won't claim to have fully reviewed it though.

[igloo]

This proposal seems to be abandoned

[bos]

This was actually shipped in, I think, 6.8.1.