libsyntax: Implement deriving correctly for type-parameterized structs and enums. r=brson

src/test/run-pass/deriving-via-extension-type-params.rs

@@ -0,0 +1,17 @@
+#[deriving_eq]
+#[deriving_iter_bytes]
+struct Foo<T> {
+    x: int,
+    y: T,
+    z: int
+}
+
+fn main() {
+    let a = Foo { x: 1, y: 2.0, z: 3 };
+    let b = Foo { x: 1, y: 2.0, z: 3 };
+    assert a == b;
+    assert !(a != b);
+    assert a.eq(&b);
+    assert !a.ne(&b);
+}
+