Update to rustfmt-preview (#348)

* Update to rustfmt-preview.

* Run "cargo fmt --all" with rustfmt 0.4.1.

rustfmt 0.4.1 is the latest release of rustfmt-preview available on the
stable channel.

* Fix a long line that rustfmt 0.4.1 can't handle.

* Remove unneeded commas left behind by rustfmt.

lib/filetests/src/test_postopt.rs

@@ -37,14 +37,12 @@ impl SubTest for TestPostopt {
         let isa = context.isa.expect("postopt needs an ISA");
 
         comp_ctx.flowgraph();
-        comp_ctx.postopt(isa).map_err(|e| {
-            pretty_error(&comp_ctx.func, context.isa, Into::into(e))
-        })?;
+        comp_ctx
+            .postopt(isa)
+            .map_err(|e| pretty_error(&comp_ctx.func, context.isa, Into::into(e)))?;
 
         let mut text = String::new();
-        write!(&mut text, "{}", &comp_ctx.func).map_err(
-            |e| e.to_string(),
-        )?;
+        write!(&mut text, "{}", &comp_ctx.func).map_err(|e| e.to_string())?;
         run_filecheck(&text, context)
     }
 }