assert_redirected_to does not show user-supplied message (in 3.* branch)

[907th]

Issue: when assert_redirected_to fails due to the response redirect not
matching the expected redirect the user-supplied message (second parameter)
is not shown. This message is only shown if the response is not a redirect.

If ...

assert_redirected_to login_path, "Expected redirect to login page"

... there is redirection not to login_path then we don't see "Expected redirect to login page." but only default "Expected response to be a redirect to /login but was a redirect to /other." message.

The issue was first mentioned in 2011 but was not fixed in 3.* branch. I faced with it several days ago.

In 4.* action_dispatch tests helpers were refactored so 4.* has no such bug.