Use default similarity of 3/4 (fourth quartile) instead of 0.8

The choice of 0.8 or 80% was fairly arbitrary and mostly a good
first guess but 0.75 as 3/4 is slightly more forgiving of changes
and easier to keep in mind.

guibot/finder.py

@@ -342,7 +342,7 @@ def __configure_backend(self, backend=None, category="find", reset=False):
         log.log(9, "Setting backend for %s to %s", category, backend)
         self.params[category] = {}
         self.params[category]["backend"] = backend
-        self.params[category]["similarity"] = CVParameter(0.8, 0.0, 1.0)
+        self.params[category]["similarity"] = CVParameter(0.75, 0.0, 1.0)
         log.log(9, "%s %s\n", category, self.params[category])
 
     def configure_backend(self, backend=None, category="find", reset=False):

tests/test_target.py

@@ -87,7 +87,7 @@ def test_similarity(self):
         new_image = image.with_similarity(0.45)
         self.assertEqual(0.45, new_image.similarity)
         # TODO: create a separate config for defaults to extract this from there
-        self.assertEqual(0.8, image.similarity)
+        self.assertEqual(0.75, image.similarity)
 
         self.assertEqual(image.filename, new_image.filename)
         self.assertNotEqual(image.similarity, new_image.similarity)