Unfortunately, I completely missed the host argument to is_safe_url.
Without it, the check will have always returned False (see #1557).

This change fixes this behaviour. Unfortunately, it does require
changing the notation of the safe_referrer and redirect_to_referrer
utility functions.

They are from a time when we had one stockrecord per product, and no
strategy classes. They're used for visual purposes only, and were
forgotten when the codebase was updated. They failed loudly, as reported
in #1592.

We really need to either drop them or add a helper method to the
strategy class, but to ensure backwards-compatibility, I've
re-implemented the naive approach of just sorting by price; blindly
ignoring the many shortcomings.

I also added a deprecation notice.

They got shifted by accident in 1023401c

Backport of 58e91e6 from master.

A simple typo lead to star imports not working as expected. As it's
easily worked around, we won't issue a release right away.

Closes #1553.

(cherry picked from commit 80babf2c19)

Conflicts:
	docs/source/releases/index.rst

A simple typo lead to star imports not working as expected. As it's
easily worked around, we won't issue a release right away.

Closes #1553.