Fix HTML content detection

[Alex-302]

• cowcotland.com
  http://www.cowcotland.com/config.html

http://www.cowcotland.com/scripjs.php?files=jquery,jquery.easing.1.3

сontent-type text/html, but contains only js, without valid html tags
https://gist.github.com/Alex-302/8aa382fb3324da5349cd

• https://www.minnetonkamoccasin.com/women/styles/slippers/cally/
  injected to

https://www.minnetonkamoccasin.com/colorswatch/json/pull/

response: https://gist.github.com/Alex-302/55ba0ca087a195dac6c3

• https://cupsservice.com/Double+Wall+Paper+Cups
  when click on items
  broken XHR:

https://cupsservice.com/Double+Wall+Paper+Cups

response:
https://gist.github.com/Alex-302/653822881147a8b3c0cc

• origin.com
  injects to js(content-type: text/html)

https://eaassets01-a.akamaihd.net/origin-com-store-webassets/1.0.0.410277_856d9a751163136d6a24075ada5f26dd2db13523050d56cab862536e02d823e0/js/ea5d46c.js

response:
https://gist.github.com/Alex-302/54524224b28dae2e241e

• https://www.watersidenursery.co.uk
  When checkout(postindex for example B35 7NW)

https://www.watersidenursery.co.uk/shop/onepagecheckout/onepage/updateData/

Response
https://gist.github.com/Alex-302/21ba2cbe8adce51f6180

• http://www.aipa.ru/192-raskraski-po-nomeram
  broken ajax when click "Next page"

http://www.aipa.ru/modules/blocklayered/blocklayered-ajax.php?id_category_layered=192&orderby=date_add&orderway=desc&n=20&p=1&_=1455181164940

Response
https://gist.github.com/Alex-302/76a25da989cafbb7c11c
content-type: text/html; charset=utf-8

[Alex-302]

• https://transfers.privatbank.ua/payout/Payout/FieldsForSearchTransferFilled Broken payout
  http://pastebin.com/LDmLjntS

[ameshkov]

Fixed, review ID:
CR-AG-737