Fix some struct-tuple def prettyprint issues

- Removed space between struct name and parentheses
- Fixed indentation of the rest of the file (missing end)
- Don't print parentheses for structs with no fields
- Added test

src/test/pretty/struct-tuple.rs

@@ -0,0 +1,10 @@
+// pp-exact
+struct Foo;
+struct Bar(int, int);
+
+fn main() {
+    struct Foo2;
+    struct Bar2(int, int, int);
+    let a = Bar(5, 5);
+    let b = Foo;
+}