deny warnings and unsafe code in tests and examples

tests/cfail/resource-not-send.rs

+#![deny(unsafe_code)]
 #![deny(warnings)]
 #![feature(const_fn)]
 #![feature(proc_macro)]

tests/cfail/token-outlive.rs

+#![deny(unsafe_code)]
 #![deny(warnings)]
 #![feature(const_fn)]
 #![feature(proc_macro)]

tests/cfail/token-transfer.rs

+#![deny(unsafe_code)]
 #![deny(warnings)]
 #![feature(const_fn)]
 #![feature(proc_macro)]

tests/cfail/wrong-threshold.rs

+#![deny(unsafe_code)]
 #![deny(warnings)]
 #![feature(proc_macro)]
 #![no_std]