Panickers: PROVE or REMOVE

[gavofyork]

.expect and assert! should all have strings of the form:

"<truth> ( [, <truth>] ... ) ( [; so <derivation>] ... ); qed"

e.g.

fn foo(x: Option<int>) -> int {
    let mut b = false;
    if x.is_some() {
        b = bar();
    }

    if b {
        return x.expect("`b` initially `false`; `b` changed only inside block guarded by `x.is_some()`; `b` is `true`; so `x` must be `Some`; qed") - 1;
    }

    0
}

Any other panickers (e.g. subscripting) must have an additional assert! prepended so they fail with an error message as early as possible.

• blockchain module
• trie module
• other modules