configure: Don't build bsd-user on Mac OS X by default

Fixes the build when combined with the drop of darwin-user.
Enthusiasts can still try building it using --enable-bsd-user.

Signed-off-by: Andreas Färber <andreas.faerber@web.de>
Cc: Bernhard Walle <bernhard@bwalle.de>
Tested-by: Bernhard Walle <bernhard@bwalle.de> [Mac OS 10.7.3]
Acked-by: Bernhard Walle <bernhard@bwalle.de>
Signed-off-by: Blue Swirl <blauwirbel@gmail.com>

configure

@@ -498,8 +498,8 @@ esac
 if [ "$bsd" = "yes" ] ; then
   if [ "$darwin" != "yes" ] ; then
     usb="bsd"
+    bsd_user="yes"
   fi
-  bsd_user="yes"
 fi
 
 : ${make=${MAKE-make}}