[rust-dev] Removing ~"foo"

Hi everyone, I'd like to remove the `~"foo"` literal syntax for owned strings in both expressions and patterns. After dynamically sized types, this syntax is the last remnant of the strange parser behavior by which the parser does something different for `~"foo"` and `~("foo")` (i.e. by which it looks at the next token when it sees a sigil and does something different than it would otherwise). The new replacement for `~"foo"` will be `"foo".to_owned()`. You can also use the `fmt!()` macro or the `.to_str()` function. Post-DST, you will likely also be able to write `Heap::from("foo")`. This has no effect on constants since `~"foo"` is not allowed there anyway. Patrick