Update webappsec-charter-2015.html

Add PFWG for accessibility review
Update webappsec-charter-2015.html

Add WebApps, TPWG
Merge pull request #115 from w3c/wseltzer

W3M reviewers suggest additional liasions
`Authorization` is the header likely to be seen, not `WWW-Authenticate`

During a quick review of my SRI patch for Firefox, one of the network
engineers pointed this out:

> Checking for WWW-Authenticate is a non-sense.  It will never pop-up
> here.  Only when credentials are not provided and the channel just
> propagates the 401 response in which case the load fails anyway.
>
> You should rather check for the "Authorization" request header.

Assuming this is also the case in Chrome, we should change the
spec to make it easier for implementers.
Merge pull request #108 from fmarier/rename-www-authenticate

Check `Authorization` header in addition to `WWW-Authenticate`
Add a note about file URIs (fixes #106)

Web authors may not realize that testing integrity protection is
not going to work if they do so on their local machine using
file:/// URLs.
Merge pull request #117 from fmarier/file-uri-warning

Add a note about file URIs (fixes #106)
REFERRER: s/referer/Referer/g
MIX: Reformating links after tabatkins/bikeshed#227