std: Internalize almost all of std::rt

This commit does some refactoring to make almost all of the `std::rt` private.
Specifically, the following items are no longer part of its API:

* DEFAULT_ERROR_CODE
* backtrace
* unwind
* args
* at_exit
* cleanup
* heap (this is just alloc::heap)
* min_stack
* util

The module is now tagged as `#[doc(hidden)]` as the only purpose it's serve is
an entry point for the `panic!` macro via the `begin_unwind` and
`begin_unwind_fmt` reexports.

src/libstd/sys/unix/mod.rs

@@ -12,6 +12,7 @@
 #![allow(non_camel_case_types)]
 
 use io::{self, ErrorKind};
+use libc::funcs::posix01::signal::signal;
 use libc;
 use num::One;
 use ops::Neg;
@@ -47,6 +48,19 @@ pub mod thread_local;
 pub mod time;
 pub mod stdio;
 
+pub fn init() {
+    // By default, some platforms will send a *signal* when a EPIPE error
+    // would otherwise be delivered. This runtime doesn't install a SIGPIPE
+    // handler, causing it to kill the program, which isn't exactly what we
+    // want!
+    //
+    // Hence, we set SIGPIPE to ignore when the program starts up in order
+    // to prevent this problem.
+    unsafe {
+        assert!(signal(libc::SIGPIPE, libc::SIG_IGN) != !0);
+    }
+}
+
 pub fn decode_error_kind(errno: i32) -> ErrorKind {
     match errno as libc::c_int {
         libc::ECONNREFUSED => ErrorKind::ConnectionRefused,