Made fail! and assert! accept both &'static str and ~str, as well as a fmt! like format list.

Unwinding through macros now happens as a call to the trait function `FailWithCause::fail_with()`, which consumes self, allowing to use a more generic failure object in the future.

src/test/compile-fail/die-not-static.rs

@@ -0,0 +1,7 @@
+// error-pattern:illegal borrow: borrowed value does not live long enough
+
+fn main() {
+    let v = ~"test";
+    let sslice = str::slice(v, 0, v.len());
+    fail!(sslice);
+}

src/test/compile-fail/die-not-unique.rs

@@ -1,5 +0,0 @@
-// error-pattern:mismatched types
-
-fn main() {
-    fail!("test");
-}

src/test/compile-fail/fail-expr.rs

@@ -8,6 +8,6 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-// error-pattern:mismatched types
+// error-pattern:failed to find an implementation of trait core::sys::FailWithCause for int
 
 fn main() { fail!(5); }

src/test/compile-fail/fail-type-err.rs

@@ -8,5 +8,5 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-// error-pattern:expected `~str` but found `~[int]`
+// error-pattern:failed to find an implementation of trait core::sys::FailWithCause for ~[int]
 fn main() { fail!(~[0i]); }