ETag If-None-Match comparison must be weak

When a request is received with a If-None-Match header, the ETag comparison must be weak, according to RFC7232 § 3.2: (emphasis original)

A recipient MUST use the weak comparison function when comparing entity-tags for If-None-Match (Section 2.3.2), since weak entity-tags can be used for cache validation even if there have been changes to the representation data.

Earlier § 2.3.2 gives a helpful table for the differences between strong and weak validation:

The example below shows the results for a set of entity-tag pairs and
both the weak and strong comparison function results:

+--------+--------+-------------------+-----------------+
| ETag 1 | ETag 2 | Strong Comparison | Weak Comparison |
+--------+--------+-------------------+-----------------+
| W/"1"  | W/"1"  | no match          | match           |
| W/"1"  | W/"2"  | no match          | no match        |
| W/"1"  | "1"    | no match          | match           |
| "1"    | "1"    | match             | match           |
+--------+--------+-------------------+-----------------+

CouchDB currently uses strong comparison, even for If-None-Match.

$ curl -vo /dev/null http://couchdb.local/db/document1 -H'If-None-Match:"8FTYH1N3L0TPD7ZEZCPW16J4T"'

[…snip…]

< HTTP/1.1 304 Not Modified
< Server: CouchDB/1.6.1 (Erlang OTP/18)
< ETag: "8FTYH1N3L0TPD7ZEZCPW16J4T"
< Date: Tue, 26 Jan 2016 19:47:46 GMT
< Content-Length: 0

$ curl -vo /dev/null http://couchdb.local/db/document1 -H'If-None-Match:W/"8FTYH1N3L0TPD7ZEZCPW16J4T"'

[…snip…]

< HTTP/1.1 200 OK
< Vary: Accept
< Server: CouchDB/1.6.1 (Erlang OTP/18)
< Etag: "8FTYH1N3L0TPD7ZEZCPW16J4T"
< Date: Tue, 26 Jan 2016 19:49:25 GMT
< Content-Type: application/json
< Content-Length: 1449