fs::create_dir_all fails for directory junctions on Windows

[alexcrichton]

First reported in rust-lang/cargo#1749, it looks like if an intermediate directory is a junction on Windows then fs::create_dir_all will fail. Unfortunately the standard library doesn't provide away to create a junction, but a setup like this should work:

mkdir foo
mklink /J bar foo

use std::fs;
fs::create_dir_all("bar/test").unwrap() // this fails

[alexcrichton]

The Cargo report claims this was a regression, so I'm going to nominate this.

[alexcrichton]

I suspect fs::metadata(&junction).is_dir() is returning false (when it should perhaps return true), but I have not had a chance to investigate this too closely.

[alexcrichton]

triage: P-high