fix build

fixes:
- warning , line with more than 100 chars on align_columns.rs
- changed syntax on subslice match on 24_game_solve.rs (see pull 17054 on rust-lang/rust)
- uint overflow on luhn_test.rs


@utkarshkukreti there might be, but I don't know of one...

I looked at the [syntax for string literals on the manual](http://doc.rust-lang.org/rust.html#character-and-string-literals) but I have not found a way to split a long string into separate lines. I mean you *can* have a multi-line string, but then newlines become part of the string itself.