Proxy supports multiple headers with same name

[Alexibu]

Failing test demonstrates that multiple headers with same name don't pass through proxy.
Test passes with modifications to proxy.d

[Alexibu]

BTW I don't know how to get dub to put this test in the test suite. I was running it by calling dub test in side the tests/vibe.http.proxy.copyHeaders directory.

[s-ludwig]

Looks good as far as I can see. The test case will be picked up automatically by the CI script, which just iterates through all folders in tests/.

The only thing that needs to be adjusted is the bind address/port handling in the test case. Both servers should just listen on 127.0.0.1, port 0. Then, when doing the proxy/client requests, those also can go to 127.0.0.1 and use the port returned through the HTTPListener returned from listenHTTP (like with serverAddr in line 20). The reason is that there are often multiple CI jobs running in parallel on the same machine, so that any fixed port number will eventually conflict and cause spurious test failures.

[Alexibu]

Test updated

[s-ludwig]

The test case had to be adjusted a bit, because the event loop didn't exit for some reason, but apart from that, everything looks good to merge now.