macros: `ty` matcher doesn't accept trait object types with `+` (type sums)

Code:
```
macro_rules! m {
    ($t: ty) => ()
}

fn main() {
    m!(Write + Send);
}
```

Expected result: code compiles. 

Actual result:
```
rustc 1.16.0-nightly (1a2ed98d3 2017-01-13)
error: no rules expected the token `+`
 --> <anon>:6:14
  |
6 |     m!(Write + Send);
  |              ^
```