Request incorrectly shows `Connection` header

[jkbrzt]

…even though it's not used by HTTP/2

python-hyper/hyper#83

$ http -v  https://nghttp2.org/httpbin/get

GET /httpbin/get HTTP/1.1
Accept: */*
Accept-Encoding: gzip, deflate
Connection: keep-alive
Host: nghttp2.org
User-Agent: HTTPie/0.9.1

HTTP/2 200
access-control-allow-credentials: true
access-control-allow-origin: *
content-length: 268
content-type: application/json
date: Sat, 07 Feb 2015 17:02:52 GMT
server: nghttpx nghttp2/0.7.4-DEV
strict-transport-security: max-age=31536000
via: 1.1 nghttpx

[Lukasa]

When does HTTPie print the headers? I can't touch the request until it gets very low down indeed: the send method of the adapter. If it's printed any time before then I can't manipulate it appropriately.