[whatwg] hash Attribute

Michel Fortin wrote:
> Charles Iliya Krempeaux suggested to include the hash as an HTTP header.
> This would cover the case of an error in the transmission of a document,
> but it wouldn't in the case a file got maliciously modified on the
> server. ...

Additionally, this case is already covered by the HTTP spec, namely the
Content-MD5 header:

http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.15

Admittedly it only supports MD5 checksums; whether this is worth
extending is another matter.

Best regards
Tom Pike