Multiple mio tests leak memory on Windows

[dtacalau]

The following test suites leak memory when run under drmemory:

• close_on_drop
• tcp_stream
• poll
• tcp
• registering
• tcp_listener
• udp_socket

To run a test suite under drmemory, for instance for registering.rs:

cargo build
cargo test --test=registering
drmemory.exe target/debug/registering-6c7ff7e724cc4caa.exe

drmemory will report direct and possible leaks:

Application cmdline: "target/debug/registering-6c7ff7e724cc4caa.exe"
Recorded 117 suppression(s) from default C:\Program Files (x86)\Dr. Memory\bin64\suppress-default.txt

Error #18: LEAK 136 direct bytes 0x000000b738fd6220-0x000000b738fd62a8 + 56 indirect bytes
# 0 replace_RtlAllocateHeap                                                  [d:\drmemory_package\common\alloc_replace.c:3771]
# 1 alloc::alloc::alloc                                                      [/rustc/625451e376bb2e5283fc4741caa0a3e8a2ca4d54\src\liballoc\alloc.rs:84]
# 2 alloc::boxed::{{impl}}::call_once<>                                      [/rustc/625451e376bb2e5283fc4741caa0a3e8a2ca4d54\src\liballoc\boxed.rs:787]
# 3 panic_unwind::__rust_maybe_catch_panic                                   [/rustc/625451e376bb2e5283fc4741caa0a3e8a2ca4d54\/src\libpanic_unwind\lib.rs:80]
# 4 test::run_test::run_test_inner::{{closure}}                              [/rustc/625451e376bb2e5283fc4741caa0a3e8a2ca4d54\/src\libtest\lib.rs:1408]
# 5 std::sys_common::backtrace::__rust_begin_short_backtrace<>               [/rustc/625451e376bb2e5283fc4741caa0a3e8a2ca4d54\src\libstd\sys_common\backtrace.rs:77]
# 6 core::ops::function::FnOnce::call_once<>                                 [/rustc/625451e376bb2e5283fc4741caa0a3e8a2ca4d54\src\libcore\ops\function.rs:235]
# 7 alloc::boxed::{{impl}}::call_once<>                                      [/rustc/625451e376bb2e5283fc4741caa0a3e8a2ca4d54\src\liballoc\boxed.rs:787]
# 8 std::sys::windows::thread::{{impl}}::new::thread_start                   [/rustc/625451e376bb2e5283fc4741caa0a3e8a2ca4d54\/src\libstd\sys\windows\thread.rs:47]
# 9 KERNEL32.dll!BaseThreadInitThunk                                        +0x21     (0x00007ffc1dc513d2 <KERNEL32.dll+0x13d2>)

ERRORS FOUND:
      1 unique,     3 total,    552 byte(s) of leak(s)

These leaks seem to appear in different scenarios than the one reported here #1146:

We need to revisit these after fixing #1146 and/or #1149

[dtacalau]

After merging PR #1154, there are no more leaks. This commits 3d654f7 fixed them all.

Closing as duplicate of #1146 .