std::io::process test: ensure that path_val outlives the container that borrows it.

(part of fallout from new destructor lifetime rules.)

Author: pnkfelix

src/libstd/io/process.rs

@@ -1065,13 +1065,13 @@ mod tests {
     #[test]
     fn test_override_env() {
         use os;
+        let path_val: String;
         let mut new_env = vec![("RUN_TEST_NEW_ENV", "123")];
 
         // In some build environments (such as chrooted Nix builds), `env` can
         // only be found in the explicitly-provided PATH env variable, not in
         // default places such as /bin or /usr/bin. So we need to pass through
         // PATH to our sub-process.
-        let path_val: String;
         match os::getenv("PATH") {
             None => {}
             Some(val) => {