rustc error when file can't be opened is ugly

[brson]

brian@brianX1:~⟫ rustc foeu
error: couldn't read foeu: IoError { kind: FileNotFound, desc: "couldn\'t open path as file", detail: Some("no such file or directory (No such file or directory); path=foeu; mode=open; access=read") }

It should probably be displaying just the detail.

[rylev]

I'll try to tackle this.

[alexcrichton]

Fixed in #21336