Not finding enough backlinks

[calpaterson]

Description

Not all backlinks are being found

Steps to reproduce

1. Bookmark A, which links to B
2. Bookmark B

Expected result

A and B are linked together via links and backlinks

Actual result

Often they are not linked, for various reasons, including:

• the url of B differs slightly (eg, no trailing slash) and there is no canonical url in B to help disambiguate
• there is a canonical url, but only as open graph metadata, not as rel="canonical"
• redirects (particularly due to tracking crap)

Additional details

Probably need to split this into two or more bugs for each cause