[Bug-XBoard] xboard crashes when not invoked from shell

[h.g. muller]

Hi,

We stumbled on a nasty bug in xboard: when xboard was started up by a 
tournament manager
(in particular PSWBTM), rather than from the command line, it failed to 
work properly: the engine
it started up would always terminate immediatey after its own initialization.

We could trace the problem to the xboard code for setting up the pipes 
between GUI and engine.
This code is not resistent to file descriptors 0 or 1 being initially 
closed. Ans some software
packages, including the wxWidgets on which PSWBTM was based, close all 
unused file descriptors
on executing another program. So when launched from PSWBTM, xboard was 
started with file
descriptor 1 closed.

The code of 4.2.7 first creates the pipes (which will obtain the 
lowest-available file descriptors),
then duplicates them to 0 and 1, then closes the original pipe descriptors. 
But if 1 was amongst the
latter, it means one of the newly setup pipes is closed again.

In xboard 4.3.15 (the upcoming release in my own development branch) I have 
fixed this by moving
the close() calls for the unused pipe ends to before the dup2() calls. In 
the closing of the original
pipe descriptors after duplication one has to be more careful, and only 
close them if they are >= 2.
As expected, this cures the problem, and make xboard run under PSWBTM on 
Linux like WinBoard
does on Windows. (PSWBTM is platform independent.)

Regards,
H.G.