Copy canonical/shortlink/shorturl as url if it exist in header.

This change is to copy shorturl or canonical link of web page by default.

For example -
http://www.amazon.co.jp/gp/product/B00CTUMNAO/ref=kp_jl_2/377-9059291-7139359?pf_rd_m=AN1VRQENFRJN5&pf_rd_s=gateway-center-column&pf_rd_r=0KCVPM04WXPH7XVF4DVF&pf_rd_t=101&pf_rd_p=146484869&pf_rd_i=489986
http://www.amazon.co.jp/Amazon-53-000955-Kindle-Paperwhite%EF%BC%88%E3%83%8B%E3%83%A5%E3%83%BC%E3%83%A2%E3%83%87%E3%83%AB%EF%BC%89/dp/B00CTUMNAO

http://www.youtube.com/watch?v=4Ahi7gRz87o
http://youtu.be/4Ahi7gRz87o

Ref
* Official Google Webmaster Central Blog: Specify your canonical http://googlewebmastercentral.blogspot.tw/2009/02/specify-your-canonical.html
* About rel="canonical" - Webmaster Tools Help https://support.google.com/webmasters/answer/139394?hl=en
* shorturl auto-discovery - a standard for URL shortening http://relshorturl.appspot.com/
* rel="shortlink" · Microformats Wiki http://microformats.org/wiki/rel-shortlink