Macro bootstrap::t

macro_rules! t {
    ($e:expr) => { ... };
    ($e:expr, $extra:expr) => { ... };
}

A helper macro to unwrap a result except also print out details like:

• The file/line of the panic
• The expression that failed
• The error itself

This is currently used judiciously throughout the build system rather than using a Result with try!, but this may change one day…