auto merge of #6487 : recrack/rust/vec_len, r=thestinger

Rename vec::len(var) to var.len()

```
libcore, libfuzzer, librustc, librustdoc, libstd, libsyntax
test/auxiliary
test/bench
test/run-pass
```

src/librustc/metadata/decoder.rs

@@ -1063,7 +1063,7 @@ fn get_attributes(md: ebml::Doc) -> ~[ast::attribute] {
             let meta_items = get_meta_items(attr_doc);
             // Currently it's only possible to have a single meta item on
             // an attribute
-            assert!((vec::len(meta_items) == 1u));
+            assert!(meta_items.len() == 1u);
             let meta_item = meta_items[0];
             attrs.push(
                 codemap::spanned {