Wrong platform check for Xinerama support

configure.in / configure.ac also contains some fishy platform checks in
the Xinerama support check:

...
elif test "$_os" = "Linux" -o "$_os" = "FreeBSD"; then
    if test "$x_libraries" = "default_x_libraries"; then
            XINERAMALIB=`$PKG_CONFIG --variable=libdir xinerama`
...

I'm not too sure of why this line was added but Linux and FreeBSD are not
the only operating systems which can use Xorg.

Maybe this should be changed to something like this ?

elif test "$_os" != "WINNT"; then

I'm reluctant to add all current Unix operating systems using Xorg to the
elif line. Does someone know what was the intended goal for this check ?

-- 
Francois Tigeot