HTTP_PROXY parsing should be more robust

[lachlan2k]

The HTTP_PROXY env variable can take many forms, such as http://my-egress-lad:1234. But, net.Dial is confused as it expects host:port, and this will cause an error.

When trying http_proxy, I suggest that RSSH should:

• Strip out http://
• If no port is specified, try both 80, and 8080

[NHAS]

This is now on unstable

[lachlan2k]

I like the changes -- perhaps they should also be applied to the --proxy command line flag? It would be great for that to be more versatile (and consistency).

I have to admit it took me a hot second to realise what was was breaking when I was trying to --proxy http://foo previously.

I'll test later to make sure it works for me.

[NHAS]

Done