Fix compiler warning on shift overflow.

In file included from /Users/erik/dev/qt5-stable/qtbase/include/QtXmlPatterns/5.0.0/QtXmlPatterns/private/qcoloroutput_p.h:1:
/Users/erik/dev/qt5-stable/qtbase/include/QtXmlPatterns/5.0.0/QtXmlPatterns/private/../../../../../../qtxmlpatterns/src/xmlpatterns/api/qcoloroutput_p.h:74:60: warning: signed
      shift result (0xFFFFF00000) requires 41 bits to represent, but 'int' only has 32 bits [-Wshift-overflow]
            BackgroundMask  = ((1 << BackgroundShift) - 1) << BackgroundShift
                              ~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ^  ~~~~~~~~~~~~~~~

Change-Id: Id8b1d9748dd94350d42889b36c61c163786beb38
Reviewed-by: Lars Knoll <lars.knoll@digia.com>

src/xmlpatterns/api/qcoloroutput_p.h

@@ -71,7 +71,7 @@ namespace QPatternist
             BackgroundShift = 20,
             SpecialShift    = 20,
             ForegroundMask  = ((1 << ForegroundShift) - 1) << ForegroundShift,
-            BackgroundMask  = ((1 << BackgroundShift) - 1) << BackgroundShift
+            BackgroundMask  = ((1 << (sizeof(int) - BackgroundShift)) - 1) << BackgroundShift
         };
 
     public: