Convert most working tests to ivecs

I tried to pay attention to what was actually being tested so, e.g. when I
test was just using a vec as a boxed thing, I converted to boxed ints, etc.

Haven't converted the macro tests yet. Not sure what to do there.

src/test/compile-fail/writing-through-uninit-vec.rs

@@ -1,5 +1,5 @@
 // error-pattern: Unsatisfied precondition constraint
 
-fn test() { let w: vec[int]; w.(5) = 0; }
+fn test() { let w: [int]; w.(5) = 0; }
 
 fn main() { test(); }