Custom cookie hash

[hmphu]

Hi,

I had problem when using specific cookie to check and change the magento design package.

When people visit my site using a mobile device they will see a link "View desktop version", when they click that link I set a cookie USE_FULL_SITE=1 then check and change the design package. In desktop version they will see a link "View mobile version" but when they click that link and I set USE_FULL_SITE=0, varnish return the same page.

This PR add ability to add custom cookie key to the varnish hash, I created a configuration field in Admin > System > Configurations > Turpentine > Caching Options > Cookie-based Caching > Cookie Keys

I think people who use cookie to check and display/hide popup will have the same issue

Please consider to merge.

Thanks a lot,
Phu

[jeroenvermeulen]

Looks good (did not test it)