Fix a error caused by my previous merging operation.
Add comments about traincascade.
Merge branch 'mycascade' of https://github.com/cook/opencv into mycascade

# Please enter a commit message to explain why this merge is necessary,
# especially if it merges an updated upstream into a topic branch.
#
# Lines starting with '#' will be ignored, and an empty message aborts
# the commit.
Merge branch 'mycascade' of https://github.com/cook/opencv into mycascade