std: Minor cleanup to libtest

[alexcrichton]

• Don't spawn two threads for all tests, just one now that catch_unwind is
  stable.
• Remove usage of the unstable box keyword
• Remove usage of the unstable FnBox trait

[rust-highfive]

r? @sfackler

(rust_highfive has picked a reviewer for you, use r? to override)

[sfackler]

r=me but travis is failing

[alexcrichton]

@bors: r=sfackler

[bors]

📌 Commit 4f1eccc has been approved by sfackler

[TimNN]

Still fails travis:

error[E0281]: type mismatch: the type `[closure@src/tools/compiletest/src/main.rs:467:30: 469:6 config:_, testpaths:_]` implements the trait `std::ops::FnOnce<()>`, but the trait `std::ops::FnOnce<((),)>` is required (expected tuple, found ())
   --> src/tools/compiletest/src/main.rs:467:21
    |
467 |     test::DynTestFn(Box::new(move || {
    |                     ^
    |
    = note: required because of the requirements on the impl of `test::FnBox<()>` for `[closure@src/tools/compiletest/src/main.rs:467:30: 469:6 config:_, testpaths:_]`
    = note: required for the cast to the object type `test::FnBox<()> + 'static`

error: aborting due to previous error

[alexcrichton]

@bors: r=sfackler

[bors]

📌 Commit e18b415 has been approved by sfackler

[alexcrichton]

@bors: r=sfackler

[bors]

📌 Commit eebe9a2 has been approved by sfackler

[sophiajt]

Seeing a fair number of errors like (which seem legit):

   Compiling test v0.0.0 (file:///build/src/libtest)
error[E0281]: type mismatch: the type `[closure@src/libtest/lib.rs:1499:40: 1499:51]` implements the trait `std::ops::FnOnce<()>`, but the trait `std::ops::FnOnce<((),)>` is required (expected tuple, found ())
    --> src/libtest/lib.rs:1499:31
     |
1499 |             testfn: DynTestFn(Box::new(move || f())),
     |                               ^^^^^^^^^^^^^^^^^^^^^
     |
     = note: required because of the requirements on the impl of `FnBox<()>` for `[closure@src/libtest/lib.rs:1499:40: 1499:51]`
     = note: required for the cast to the object type `FnBox<()> + 'static`
error[E0281]: type mismatch: the type `[closure@src/libtest/lib.rs:1516:40: 1516:51]` implements the trait `std::ops::FnOnce<()>`, but the trait `std::ops::FnOnce<((),)>` is required (expected tuple, found ())
    --> src/libtest/lib.rs:1516:31
     |
1516 |             testfn: DynTestFn(Box::new(move || f())),
     |                               ^^^^^^^^^^^^^^^^^^^^^
     |
     = note: required because of the requirements on the impl of `FnBox<()>` for `[closure@src/libtest/lib.rs:1516:40: 1516:51]`
     = note: required for the cast to the object type `FnBox<()> + 'static`
error[E0281]: type mismatch: the type `[closure@src/libtest/lib.rs:1535:40: 1535:51]` implements the trait `std::ops::FnOnce<()>`, but the trait `std::ops::FnOnce<((),)>` is required (expected tuple, found ())
    --> src/libtest/lib.rs:1535:31
     |
1535 |             testfn: DynTestFn(Box::new(move || f())),
     |                               ^^^^^^^^^^^^^^^^^^^^^
     |
     = note: required because of the requirements on the impl of `FnBox<()>` for `[closure@src/libtest/lib.rs:1535:40: 1535:51]`
     = note: required for the cast to the object type `FnBox<()> + 'static`

[alexcrichton]

@bors: r=sfackler

[bors]

📌 Commit 0714024 has been approved by sfackler

[bors]

⌛ Testing commit 0714024 with merge 6e8f92f...

[bors]

☀️ Test successful - auto-linux-32-nopt-t, auto-linux-32-opt, auto-linux-64-cargotest, auto-linux-64-cross-freebsd, auto-linux-64-debug-opt, auto-linux-64-nopt-t, auto-linux-64-opt, auto-linux-64-opt-rustbuild, auto-linux-64-x-android-t, auto-linux-cross-opt, auto-linux-musl-64-opt, auto-mac-32-opt, auto-mac-64-opt, auto-mac-64-opt-rustbuild, auto-mac-cross-ios-opt, auto-win-gnu-32-opt, auto-win-gnu-32-opt-rustbuild, auto-win-gnu-64-opt, auto-win-msvc-32-opt, auto-win-msvc-64-cargotest, auto-win-msvc-64-opt, auto-win-msvc-64-opt-rustbuild
Approved by: sfackler
Pushing 6e8f92f to master...