Fixed processing of atom links without a ‘rel’ attribute.

[nmdias]

Atom links that had no rel' attribute weren't being processed.

http://tools.ietf.org/html/rfc4287#page-21

4.2.7.2. The "rel" Attribute atom:link elements MAY have a "rel" attribute that indicates the link relation type. If the "rel" attribute is not present, the link element MUST be interpreted as if the link relation type is "alternate".