Use static string with fail!() and remove fail!(fmt!())

fail!() used to require owned strings but can handle static strings
now. Also, it can pass its arguments to fmt!() on its own, no need for
the caller to call fmt!() itself.
Fix cosmetics for fail!() calls
auto merge of #6357 : dotdash/rust/fixfmt, r=bstrie

fail!() used to require owned strings but can handle static strings
now. Also, it can pass its arguments to fmt!() on its own, no need for
the caller to call fmt!() itself.