Make the getenv(3) declaration visible.

--- ballandpaddle-0.8.1/src/settingsmanager.cpp	2009-07-08 02:13:16.000000000 +0200
+++ ballandpaddle-0.8.1/src/settingsmanager.cpp	2009-07-16 23:30:28.000000000 +0200
@@ -17,6 +17,7 @@
  *  along with this program.  If not, see <http://www.gnu.org/licenses/>.
  **/
 
+#include <stdlib.h>
 #include "settingsmanager.h"
 
 SettingsManager::SettingsManager ()