Macro assert_relative_ne

macro_rules! assert_relative_ne {
    ($given:expr, $expected:expr $(, $opt:ident = $val:expr)*) => { ... };
    ($given:expr, $expected:expr $(, $opt:ident = $val:expr)*,) => { ... };
}

An assertion that delegates to relative_ne!, and panics with a helpful error on failure.