Redox support

[jackpot51]

Redox uses file: at the beginning of any file paths. Therefore, a path like file:///home/user/some%20file.txt needs to turn into file:/home/user/some file.txt

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This change is 

[SimonSapin]

The initial value of bytes is the only difference with the Unix variant of this function, right? I’d prefer we keep a single function and use something like let mut bytes = if cfg!(target_os = "redox") { b"file:".to_vec() } else { Vec::new() };, to reduce code duplication.

Does the path_to_file_url_segments function need any corresponding change?

[jackpot51]

Good point, I can do that

[jackpot51]

I will check path_to_file_url_segments

[jackpot51]

I cleaned up the patch. It is the best I can do so far. There is not much I can do with path_to_file_url_segments until this issue is solved: rust-lang/rust#52331

I would recommend that this PR is merged and I can create an issue to update the other function when possible.

[SimonSapin]

Thanks!

@bors-servo r+

[bors-servo]

📌 Commit 01404b7 has been approved by SimonSapin

[bors-servo]

⌛ Testing commit 01404b7 with merge a1d8c88...

[bors-servo]

☀️ Test successful - checks-travis
Approved by: SimonSapin
Pushing a1d8c88 to master...