Renamed ast::Purity to ast::FnStyle and ast::ImpureFn to ast::NormalFn and updated associated variable and function names.

src/test/compile-fail/trait-impl-method-mismatch.rs

@@ -17,7 +17,7 @@ trait Mumbo {
 impl Mumbo for uint {
     // Cannot have a larger effect than the trait:
     unsafe fn jumbo(&self, x: @uint) { *self + *x; }
-    //~^ ERROR expected impure fn but found unsafe fn
+    //~^ ERROR expected normal fn but found unsafe fn
 }
 
 fn main() {}