Add parser support for generalized where clauses

Implement support in the parser for generalized where clauses,
as well as the conversion of ast::WherePredicates to
ty::Predicate in `collect.rs`.

src/test/compile-fail/where-clause-constraints-are-local-for-trait-impl.rs

@@ -0,0 +1,33 @@
+// Copyright 2014 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+fn require_copy<T: Copy>(x: T) {}
+
+struct Bar<T> { x: T }
+
+trait Foo<T> {
+    fn needs_copy(self) where T: Copy;
+    fn fails_copy(self);
+}
+
+// Ensure constraints are only attached to methods locally
+impl<T> Foo<T> for Bar<T> {
+    fn needs_copy(self) where T: Copy {
+        require_copy(self.x);
+
+    }
+
+    fn fails_copy(self) {
+        require_copy(self.x);
+        //~^ ERROR the trait `core::kinds::Copy` is not implemented for the type `T`
+    }
+}
+
+fn main() {}