Release builds broken with Rust 1.23.0-beta.1

[rillian]

Builds with the current rust beta fail tests:

$ rustup update beta
$ cargo +beta test --release
[...]
failures:

---- test_labels_names::test_all_labels stdout ----
	thread 'test_labels_names::test_all_labels' panicked at 'assertion failed: `(left == right)`
  left: `Some(Encoding { windows-1252 })`,
 right: `Some(Encoding { windows-1252 })`', src/test_labels_names.rs:11:4
note: Run with `RUST_BACKTRACE=1` for a backtrace.

---- tests::test_label_resolution stdout ----
	thread 'tests::test_label_resolution' panicked at 'assertion failed: `(left == right)`
  left: `Some(Encoding { UTF-8 })`,
 right: `Some(Encoding { UTF-8 })`', src/lib.rs:4419:8


failures:
    test_labels_names::test_all_labels
    tests::test_label_resolution

test result: FAILED. 106 passed; 2 failed; 0 ignored; 0 measured; 0 filtered out

error: test failed, to rerun pass '--lib'

[rillian]

See also Firefox bug 1421100.

[hsivonen]

Looks like a Rust bug.

[hsivonen]

Fixed in rustc.