Fix redox prefix handling

src/libstd/sys/redox/path.rs

@@ -21,8 +21,16 @@ pub fn is_verbatim_sep(b: u8) -> bool {
     b == b'/'
 }
 
-pub fn parse_prefix(_: &OsStr) -> Option<Prefix> {
-    None
+pub fn parse_prefix(path: &OsStr) -> Option<Prefix> {
+    if let Some(path_str) = path.to_str() {
+        if let Some(i) = path_str.find(':') {
+            Some(Prefix::Scheme(OsStr::new(&path_str[..i])))
+        } else {
+            None
+        }
+    } else {
+        None
+    }
 }
 
 pub const MAIN_SEP_STR: &'static str = "/";