syntax: ViewItemUse no longer contains multiple view paths.

it reflected the obsolete syntax `use a, b, c;` and did not make
past the parser (though it was a non-fatal error so we can continue).
this legacy affected many portions of rustc and rustdoc as well,
so this commit cleans them up altogether.

src/librustdoc/clean.rs

@@ -1085,7 +1085,7 @@ impl Clean<Item> for ast::ViewItem {
 #[deriving(Clone, Encodable, Decodable)]
 pub enum ViewItemInner {
     ExternCrate(~str, Option<~str>, ast::NodeId),
-    Import(Vec<ViewPath>)
+    Import(ViewPath)
 }
 
 impl Clean<ViewItemInner> for ast::ViewItem_ {
@@ -1099,7 +1099,7 @@ impl Clean<ViewItemInner> for ast::ViewItem_ {
                 ExternCrate(i.clean(), string, *id)
             }
             &ast::ViewItemUse(ref vp) => {
-                Import(vp.clean().move_iter().collect())
+                Import(vp.clean())
             }
         }
     }

src/librustdoc/html/render.rs

@@ -1165,12 +1165,10 @@ fn item_module(w: &mut Writer, cx: &Context,
                         try!(write!(w, ";</code></td></tr>"));
                     }
 
-                    clean::Import(ref imports) => {
-                        for import in imports.iter() {
-                            try!(write!(w, "<tr><td><code>{}{}</code></td></tr>",
-                                          VisSpace(myitem.visibility),
-                                          *import));
-                        }
+                    clean::Import(ref import) => {
+                        try!(write!(w, "<tr><td><code>{}{}</code></td></tr>",
+                                      VisSpace(myitem.visibility),
+                                      *import));
                     }
                 }
 

src/librustdoc/visit_ast.rs

@@ -133,14 +133,12 @@ impl<'a> RustdocVisitor<'a> {
             return om.view_items.push(item.clone());
         }
         let item = match item.node {
-            ast::ViewItemUse(ref paths) => {
-                // rustc no longer supports "use foo, bar;"
-                assert_eq!(paths.len(), 1);
-                match self.visit_view_path(*paths.get(0), om) {
+            ast::ViewItemUse(ref vpath) => {
+                match self.visit_view_path(*vpath, om) {
                     None => return,
                     Some(path) => {
                         ast::ViewItem {
-                            node: ast::ViewItemUse(vec!(path)),
+                            node: ast::ViewItemUse(path),
                             .. item.clone()
                         }
                     }