Several fixes for DragonFly (rebase)

src/libstd/sys/unix/os.rs

@@ -172,7 +172,7 @@ pub fn join_paths<T: BytesContainer>(paths: &[T]) -> Result<Vec<u8>, &'static st
     Ok(joined)
 }
 
-#[cfg(any(target_os = "freebsd", target_os = "dragonfly"))]
+#[cfg(target_os = "freebsd")]
 pub fn load_self() -> Option<Vec<u8>> {
     unsafe {
         use libc::funcs::bsd44::*;
@@ -198,6 +198,16 @@ pub fn load_self() -> Option<Vec<u8>> {
     }
 }
 
+#[cfg(target_os = "dragonfly")]
+fn load_self() -> Option<Vec<u8>> {
+    use std::io;
+
+    match io::fs::readlink(&Path::new("/proc/curproc/file")) {
+        Ok(path) => Some(path.into_vec()),
+        Err(..) => None
+    }
+}
+
 #[cfg(any(target_os = "linux", target_os = "android"))]
 pub fn load_self() -> Option<Vec<u8>> {
     use std::io;