copied helper modules from doc to modules/python/test

modules/python/test/precornerdetect.py

@@ -0,0 +1,14 @@
+import cv
+
+def precornerdetect(image):
+    # assume that the image is floating-point 
+    corners = cv.CloneMat(image)
+    cv.PreCornerDetect(image, corners, 3)
+
+    dilated_corners = cv.CloneMat(image)
+    cv.Dilate(corners, dilated_corners, None, 1)
+
+    corner_mask = cv.CreateMat(image.rows, image.cols, cv.CV_8UC1)
+    cv.Sub(corners, dilated_corners, corners)
+    cv.CmpS(corners, 0, corner_mask, cv.CV_CMP_GE)
+    return (corners, corner_mask)