rollup merge of #21678: vojtechkral/threads-native-names

Fixes #10302

I really am not sure I'm doing this right, so here goes nothing...

Also testing this isn't easy. I don't have any other *nix boxes besides a Linux one.

Test code:

```rust
use std::thread;
use std::io::timer::sleep;
use std::time::duration::Duration;

fn make_thread<'a>(i: i64) -> thread::JoinGuard<'a, ()>
{
	thread::Builder::new().name(format!("MyThread{}", i).to_string()).scoped(move ||
	{
		println!("Start: {}", i);
		sleep(Duration::seconds(i));
		println!("End: {}", i);
	})
}

fn main()
{
	let mut guards = vec![make_thread(3)];

	for i in 4i64..16
	{
		guards.push(make_thread(i));
	}
}
```

GDB output on my machine:

```
(gdb) info threads
  Id   Target Id         Frame
  15   Thread 0x7fdfbb35f700 (LWP 23575) "MyThread3" 0x00007fdfbbe35a8d in nanosleep () from /usr/lib/libpthread.so.0
  14   Thread 0x7fdfba7ff700 (LWP 23576) "MyThread4" 0x00007fdfbbe35a8d in nanosleep () from /usr/lib/libpthread.so.0
  13   Thread 0x7fdfba5fe700 (LWP 23577) "MyThread5" 0x00007fdfbbe35a8d in nanosleep () from /usr/lib/libpthread.so.0
  12   Thread 0x7fdfba3fd700 (LWP 23578) "MyThread6" 0x00007fdfbbe35a8d in nanosleep () from /usr/lib/libpthread.so.0
  11   Thread 0x7fdfb8dfe700 (LWP 23580) "MyThread4" 0x00007fdfbb746193 in select () from /usr/lib/libc.so.6
  10   Thread 0x7fdfb8fff700 (LWP 23579) "MyThread7" 0x00007fdfbbe35a8d in nanosleep () from /usr/lib/libpthread.so.0
  9    Thread 0x7fdfb8bfd700 (LWP 23581) "MyThread8" 0x00007fdfbbe35a8d in nanosleep () from /usr/lib/libpthread.so.0
  8    Thread 0x7fdfb3fff700 (LWP 23582) "MyThread9" 0x00007fdfbbe35a8d in nanosleep () from /usr/lib/libpthread.so.0
  7    Thread 0x7fdfb3dfe700 (LWP 23583) "MyThread10" 0x00007fdfbbe35a8d in nanosleep () from /usr/lib/libpthread.so.0
  6    Thread 0x7fdfb3bfd700 (LWP 23584) "MyThread11" 0x00007fdfbbe35a8d in nanosleep () from /usr/lib/libpthread.so.0
  5    Thread 0x7fdfb2bff700 (LWP 23585) "MyThread12" 0x00007fdfbbe35a8d in nanosleep () from /usr/lib/libpthread.so.0
  4    Thread 0x7fdfb29fe700 (LWP 23586) "MyThread13" 0x00007fdfbbe35a8d in nanosleep () from /usr/lib/libpthread.so.0
  3    Thread 0x7fdfb27fd700 (LWP 23587) "MyThread14" 0x00007fdfbbe35a8d in nanosleep () from /usr/lib/libpthread.so.0
  2    Thread 0x7fdfb1bff700 (LWP 23588) "MyThread15" 0x00007fdfbbe35a8d in nanosleep () from /usr/lib/libpthread.so.0
* 1    Thread 0x7fdfbc411800 (LWP 23574) "threads" 0x00007fdfbbe2e505 in pthread_join () from /usr/lib/libpthread.so.0
```
(I'm not sure why one of the threads is duplicated, but it does that without my patch too...)

1 files changed, 4 insertions, 0 deletions

diff --git a/src/libstd/sys/common/thread_info.rs b/src/libstd/sys/common/thread_info.rs
index 92b936e74f6..7c9758ca924 100644
--- a/src/libstd/sys/common/thread_info.rs
+++ b/src/libstd/sys/common/thread_info.rs
@@ -56,6 +56,10 @@ pub fn stack_guard() -> uint {
 
 pub fn set(stack_bounds: (uint, uint), stack_guard: uint, thread: Thread) {
     THREAD_INFO.with(|c| assert!(c.borrow().is_none()));
+    match thread.name() {
+        Some(name) => unsafe { ::sys::thread::set_name(name.as_slice()); },
+        None => {}
+    }
     THREAD_INFO.with(move |c| *c.borrow_mut() = Some(ThreadInfo{
         stack_bounds: stack_bounds,
         stack_guard: stack_guard,