Print if OpenCV python is available

doc/conf.py

@@ -283,8 +283,10 @@ intersphinx_mapping = {
 try:
   import cv2
   has_opencv = True
+  print("OpenCV python module is installed - running full doctest suite")
 except ImportError:
   has_opencv = False
+  print("OpenCV python module is *NOT* installed - skipping parts")
 
 def setup(app):
   app.add_config_value('has_opencv', has_opencv, 'html')