Implement Show for CString

We use use `from_utf8_lossy` to convert it to a MaybeOwned string, to
avoid failing in case the CString contains invalid UTF-8

src/librustrt/c_str.rs

@@ -73,6 +73,7 @@ use collections::hash;
 use core::kinds::marker;
 use core::mem;
 use core::ptr;
+use core::fmt;
 use core::raw::Slice;
 use core::slice;
 use core::str;
@@ -344,6 +345,12 @@ impl Collection for CString {
     }
 }
 
+impl fmt::Show for CString {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        String::from_utf8_lossy(self.as_bytes_no_nul()).fmt(f)
+    }
+}
+
 /// A generic trait for converting a value to a CString.
 pub trait ToCStr {
     /// Copy the receiver into a CString.