Allow is not in 13.5.2

[mnot@…]

Section 14.7 states:

"A proxy MUST NOT modify the Allow header field even if it does not understand all the methods specified, since the user agent might have other means of communicating with the origin server."

However, section 13.5.2 (Non-modifiable Headers) makes no mention of Allow. This seems like an error, but I'm not entirely sure what the fix should be -- remove 13.5.2 and push the (not-)modifiable information in the definition of the respective headers, or to maintain 13.5.2 in parallel with all of the header definitions, or to push all the information out of the header definitions into 13.5.2.

The easy fix for now would be to just make a mention of Allow in 13.5.2.

Additionally, Server should also be included.

[julian.reschke@…]

Note: the related text is gone from P6. We probably should create a new issue for the current TODO in P6 (end-to-end and hop-by-hop headers, non-modifiable headers removed; re-spec in p1) and then close this issue, noting the new test in P1 is supposed to fix this issue.

[julian.reschke@…]

From [1245]:

Add "Allow" and "Server" to the list of headers not to be modified by proxies (see #53)