Fixes:

 * give the new feature its own feature tag
 * correct a lifetime problem in the test
 * use .output() instead of .spawn() in the test so that output is
   actually collected
 * correct the same error in the test whose skeleton I cribbed

src/libstd/process.rs

@@ -399,7 +399,7 @@ impl Command {
     ///         .spawn()
     ///         .expect("printenv failed to start");
     /// ```
-    #[stable(feature = "process", since = "1.16.0")]
+    #[stable(feature = "command_envs", since = "1.16.0")]
     pub fn envs<K, V>(&mut self, vars: &[(K, V)]) -> &mut Command
         where K: AsRef<OsStr>, V: AsRef<OsStr>
     {

src/test/run-pass/process-envs.rs

@@ -41,18 +41,17 @@ fn main() {
     let filtered_env : Vec<(String, String)> =
         env::vars().filter(|&(ref k, _)| k == "PATH").collect();
 
-    let mut cmd = env_cmd()
-        .env_clear()
-        .envs(&filtered_env);
+    let mut cmd = env_cmd();
+    cmd.env_clear();
+    cmd.envs(&filtered_env);
 
     // restore original environment
     match old_env {
         None => env::remove_var("RUN_TEST_NEW_ENV"),
         Some(val) => env::set_var("RUN_TEST_NEW_ENV", &val)
     }
 
-    let prog = cmd.spawn().unwrap();
-    let result = prog.wait_with_output().unwrap();
+    let result = cmd.output().unwrap();
     let output = String::from_utf8_lossy(&result.stdout);
 
     assert!(!output.contains("RUN_TEST_NEW_ENV"),

src/test/run-pass/process-remove-from-env.rs

@@ -46,8 +46,7 @@ fn main() {
         Some(val) => env::set_var("RUN_TEST_NEW_ENV", &val)
     }
 
-    let prog = cmd.spawn().unwrap();
-    let result = prog.wait_with_output().unwrap();
+    let result = cmd.output().unwrap();
     let output = String::from_utf8_lossy(&result.stdout);
 
     assert!(!output.contains("RUN_TEST_NEW_ENV"),