try! -> ?

Automated conversion using the untry tool [1] and the following command:

```
$ find -name '*.rs' -type f | xargs untry
```

at the root of the Rust repo.

[1]: https://github.com/japaric/untry

1 files changed, 8 insertions, 8 deletions

diff --git a/src/libstd/sys/common/backtrace.rs b/src/libstd/sys/common/backtrace.rs
index 3c84783d215..b81fb3011c7 100644
--- a/src/libstd/sys/common/backtrace.rs
+++ b/src/libstd/sys/common/backtrace.rs
@@ -46,10 +46,10 @@ pub fn log_enabled() -> bool {
 // These output functions should now be used everywhere to ensure consistency.
 pub fn output(w: &mut Write, idx: isize, addr: *mut libc::c_void,
               s: Option<&[u8]>) -> io::Result<()> {
-    try!(write!(w, "  {:2}: {:2$?} - ", idx, addr, HEX_WIDTH));
+    write!(w, "  {:2}: {:2$?} - ", idx, addr, HEX_WIDTH)?;
     match s.and_then(|s| str::from_utf8(s).ok()) {
-        Some(string) => try!(demangle(w, string)),
-        None => try!(write!(w, "<unknown>")),
+        Some(string) => demangle(w, string)?,
+        None => write!(w, "<unknown>")?,
     }
     w.write_all(&['\n' as u8])
 }
@@ -59,9 +59,9 @@ pub fn output_fileline(w: &mut Write, file: &[u8], line: libc::c_int,
                        more: bool) -> io::Result<()> {
     let file = str::from_utf8(file).unwrap_or("<unknown>");
     // prior line: "  ##: {:2$} - func"
-    try!(write!(w, "      {:3$}at {}:{}", "", file, line, HEX_WIDTH));
+    write!(w, "      {:3$}at {}:{}", "", file, line, HEX_WIDTH)?;
     if more {
-        try!(write!(w, " <... and possibly more>"));
+        write!(w, " <... and possibly more>")?;
     }
     w.write_all(&['\n' as u8])
 }
@@ -121,12 +121,12 @@ pub fn demangle(writer: &mut Write, s: &str) -> io::Result<()> {
 
     // Alright, let's do this.
     if !valid {
-        try!(writer.write_all(s.as_bytes()));
+        writer.write_all(s.as_bytes())?;
     } else {
         let mut first = true;
         while !inner.is_empty() {
             if !first {
-                try!(writer.write_all(b"::"));
+                writer.write_all(b"::")?;
             } else {
                 first = false;
             }
@@ -177,7 +177,7 @@ pub fn demangle(writer: &mut Write, s: &str) -> io::Result<()> {
                         None => rest.len(),
                         Some(i) => i,
                     };
-                    try!(writer.write_all(rest[..idx].as_bytes()));
+                    writer.write_all(rest[..idx].as_bytes())?;
                     rest = &rest[idx..];
                 }
             }