changed "exit()" to "raise SystemExit" for Jupyter Notebook functionality, clearer error message

stitching/scan.py

@@ -54,7 +54,7 @@ def get_biggest_subset(img_names, imgs, features, matches, conf_thresh=1.0, matc
     features_subset = []
     num = len(indices)
     if num < 2:
-        print('Need more images')
+        print('Need more images, no matches found!')
         raise SystemExit
     for i in range(num):
         img_subset.append(imgs[indices[i, 0]])