Avoids a name collision on Windows

since it blocks/unblocks signals

But clear the O_NONBLOCK flag if we pass this FD to another
sub-process using createProcess with UseHandle.

Importing Applicative into this module causes the instances in
Control.Monad.Instances to leak into the Haskell 98 module System,
which would break Haskell 98 programs that define these instances.

We had to do this beofre to ensure that things built in the right order,
but now Prelude is in a different package.

       
 - fix #1780: pipes created by runInteractiveProcess are set
   close-on-exec by default
 
 - add a new, more general, form of process creation: createProcess
   Each of stdin, stdout and stderr may individually be taken
   from existing Handles or attached to new pipes.  Also it
   has a nicer API (as discussed on libraries@haskell.org).
 
 - add readProcess / readProcessWithExitCode, originally from Don
   Stewart's newpopen package.  These functions behave like C's
   popen().

 - Move System.Cmd.{system,rawSystem} into System.Process.  Later
   we can depecate System.Cmd.
 
 - Don't use O_NONBLOCK for pipes, as it can confuse the process
   attached to the pipe (requires a fix to GHC.Handle in the base
   package).

 - Provide a way to close all the file descriptors in the new
   process (see #1415)

 - add a couple more tests for the new features

 - bump the version to 2.0

This makes the deps work out for the System.Posix.Signals move.

These were the cause of Hugs bug #30, I think, and weren't used by Hugs anyway.

ProcessHandle is now an MVar, in which we cache the ExitCode of the
process when we know it.

Additionally, waitForProcess and getProcessExitCode now close the
handle eagerly on Windows, this avoids a problem with hsc2hs which
wants to remove the executable it just ran, and it can't if the handle
is still open.

On Windows, attach a finalizer to the ProcessHandle so that we can
call CloseHandle() when the handle is no longer in use.  Previously we
were calling CloseHandle() in waitForProcess and terminateProcess,
which prevented making multiple calls to these functions on the same
handle.

Fixes to enable base to be compiled with -fasm on Windows:

  - a few stdcall/ccall mismatches
  - use GetTempPathA instead of GetTempPath (a couple of these)

Hugs: omit commandToProcess

runProcess: allow duplicate Handles to be passed in without deadlock.
Fixes #1187295.

Determine the location of CMD.EXE (or COMMAND.COM) using the same
algorithm as system() from msvcrt.

Fixes for Windows