kwin: Fix build failure regarding QElapsedTimer.

It seems not all Qt installs will automatically #include QElapsedTimer
from QtCore/QTimer, this caused a build failure on my system and on a
RHEL 6.2 VM I've been testing on.

Checking the Qt docs, QBasicTimer also has a separate include so
although this didn't cause a build failure, I've thrown in its
separate #include as well. I have not checked for other #include errors,
and a very quick search on b.k.o for bugs mentioning "build" did not
return any bugs to close.

I'm pretty sure this build failure applies only to master but I haven't
checked thoroughly.

composite.h

@@ -24,6 +24,8 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
 #include <QtCore/QObject>
 #include <QtCore/QTimer>
+#include <QtCore/QElapsedTimer>
+#include <QtCore/QBasicTimer>
 #include <QRegion>
 
 class KSelectionOwner;