Mechanize: Spit out 'X-Died' error, if present.

    This exposes failures caused by "twitter:card" meta infestation, and probably other things too.
Test url: http://www.bbc.co.uk/news/uk-politics-16509892
Distributions affected by example issue: optware, debian squeeze, html::parser < 3.71
To fix example issue: upgrade to HTML-Parser-3.71 or https://github.com/atomicdryad/get-flash-videos/tree/twitter_meta_tag_fix