Cleanup interfaces of Name, SyntaxContext and Ident

Make sure Name, SyntaxContext and Ident are passed by value
Make sure Idents don't serve as keys (or parts of keys) in maps, Ident comparison is not well defined

src/libsyntax/ext/base.rs

@@ -646,7 +646,7 @@ impl<'a> ExtCtxt<'a> {
         loop {
             if self.codemap().with_expn_info(expn_id, |info| {
                 info.map_or(None, |i| {
-                    if i.callee.name() == "include" {
+                    if i.callee.name().as_str() == "include" {
                         // Stop going up the backtrace once include! is encountered
                         return None;
                     }
@@ -899,9 +899,9 @@ impl SyntaxEnv {
         unreachable!()
     }
 
-    pub fn find(&self, k: &Name) -> Option<Rc<SyntaxExtension>> {
+    pub fn find(&self, k: Name) -> Option<Rc<SyntaxExtension>> {
         for frame in self.chain.iter().rev() {
-            match frame.map.get(k) {
+            match frame.map.get(&k) {
                 Some(v) => return Some(v.clone()),
                 None => {}
             }