cmp::Eq is not visible after adding basic test harness

[farcaller]

After merging in #49, tests are now broken on travis, but still work with my local rustc d0b0f16:

/home/travis/build/hackndev/zinc/src/drivers/dht22.rs:114:10: 114:36 error: binary operation `!=` cannot be applied to type `hal::gpio::Level`
/home/travis/build/hackndev/zinc/src/drivers/dht22.rs:114       if self.gpio.level() != level {
                                                                   ^~~~~~~~~~~~~~~~~~~~~~~~~~
/home/travis/build/hackndev/zinc/src/hal/gpio.rs:32:12: 32:14 error: failed to find an implementation of trait core::cmp::PartialEq for hal::gpio::Level
/home/travis/build/hackndev/zinc/src/hal/gpio.rs:32 #[deriving(Eq)]
                                                               ^~
note: in expansion of #[deriving]
/home/travis/build/hackndev/zinc/src/hal/gpio.rs:32:1: 33:4 note: expansion site

[bharrisau]

Probably due to rust-lang/rust#14534 in the new nightly.