libwaio was added due to the complete inability to cancel synchronous
I/O cleanly using the public Windows API in Windows XP. Even calling
TerminateThread on the thread performing I/O was a bad solution, because
the TerminateThread function in XP would leak the thread's stack.
In Vista and up, however, this is no longer a problem. CancelIoEx can
cancel synchronous I/O running on other threads, allowing the thread to
exit cleanly, so replace libwaio usage with native Vista API functions.
It should be noted that this change also removes the hack added in
8a27025 for preventing a deadlock that only seemed to happen in Windows
XP. KB2009703 says that Vista and up are not affected by this, due to a
change in the implementation of GetFileType, so the hack should not be
needed anymore.
Use libwaio to read from pipes (stdin or named pipes) on Windows. This
liberates us from nasty issues, such as pipes (as created by most
programs) not being possible to read in a non-blocking or event-driven
way. Although it would be possible to do that in a somewhat sane way
on Vista+, it's still not easy, and on XP it's especially hard. libwaio
handles these things for us.
Move pipe.c to pipe-unix.c, and remove Windows specific things. Also
adjust the input.c code to make this work cleanly.
