[Error] typedefs in fail(type x) blocks

Currently

``` c
typedef enum {full} full_error;
MaybeError<void,stack_error> push(int32 x) {
   return Error(full);
}
void main() {
  attempt {
    void p1 ?= push(1);
  } fail (full_error e) {
  }
}
```

The `p1` declaration doesn't resolve to the `full_error` fail block.
