pretty-printer loses parens around expr_fail in cast

[jruderman]

fn f() { (fail "boo") as float / 2.0; }

becomes

fn f() { (fail "boo" as float) / 2.0; }

which becomes

fn f() { fail "boo" as float / 2.0; }

[brson]

Added the test case, xfailed

[catamorphism]

@brson and @jruderman - Currently, this test case doesn't compile because _|_-typed things can no longer be cast to float (there's a non-scalar cast error). Is that wrong? I'm tempted to close this as obsolete, but then again, rejecting casts from _|_ to another type seems fishy.

[brson]

agreed. I removed the test from the test suite.