rollup merge of #20653: alexcrichton/entry-unstable

There's been some debate over the precise form that these APIs should take, and
they've undergone some changes recently, so these APIs are going to be left
unstable for now to be fleshed out during the next release cycle.

src/librustdoc/lib.rs

@@ -317,7 +317,7 @@ fn parse_externs(matches: &getopts::Matches) -> Result<core::Externs, String> {
             }
         };
         let name = name.to_string();
-        let locs = externs.entry(&name).get().unwrap_or_else(
+        let locs = externs.entry(name).get().unwrap_or_else(
             |vacant_entry| vacant_entry.insert(Vec::with_capacity(1)));
         locs.push(location.to_string());
     }