fixed namespace usage

felzenszwalb/segment.cpp

@@ -23,6 +23,8 @@ Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307 USA
 #include <segmentation/felzenszwalb/pnmfile.h>
 #include "segmentation/felzenszwalb/segment-image.h"
 
+using namespace felzenszwalb;
+
 int main(int argc, char **argv) {
   if (argc != 6) {
     fprintf(stderr, "usage: %s sigma k min input(ppm) output(ppm)\n", argv[0]);