pp+parser disagree about parens around "fail" in callee position

[jruderman]

This silly code fails with a type error:

fn main() { (fail)(1, 2); }

z.rs:1:12:1:18: error: mismatched types: expected function or native function but found _|_
z.rs:1 fn main() { (fail)(1, 2); }
                   ^~~~~~

but if i pretty-print it, the parens around fail are removed, and it fails with a parse error instead:

fn main() { fail(1, 2); }

z2.rs:1:18:1:19: error: expecting ), found ,
z2.rs:1 fn main() { fail(1, 2); }
                          ^

this makes the fuzzer unhappy.

I think this is a parser bug rather than a pp bug, but I'm not sure.