Enable and fix several more clippy lints.

lib/filetests/src/lib.rs

@@ -3,10 +3,20 @@
 //! This crate contains the main test driver as well as implementations of the
 //! available filetest commands.
 
+#![deny(missing_docs, trivial_numeric_casts, unused_extern_crates)]
+#![warn(unused_import_braces, unstable_features)]
 #![cfg_attr(feature="cargo-clippy", allow(
         type_complexity,
 // Rustfmt 0.9.0 is at odds with this lint:
         block_in_if_condition_stmt))]
+#![cfg_attr(feature="cargo-clippy", warn(
+                mut_mut,
+                nonminimal_bool,
+                option_map_unwrap_or,
+                option_map_unwrap_or_else,
+                unicode_not_nfc,
+                use_self,
+                ))]
 
 #[macro_use(dbg)]
 extern crate cretonne_codegen;