Make vector manipulation more efficient.

src/marshal.rs

@@ -8,12 +8,11 @@ pub fn marshal<T, F>(buf: &[u8],
                      ) -> (Vec<u8>, T)
     where F: Fn(*mut u8, *const u8, c_ulonglong) -> T {
     let mut dst = Vec::with_capacity(buf.len() + padbefore);
-    for _ in 0..padbefore {
-        dst.push(0);
-    }
-    dst.extend(buf.into_iter());
+    dst.resize(padbefore, 0u8);
+    dst.extend_from_slice(&buf[..]);
     let pdst = dst.as_mut_ptr();
     let psrc = dst.as_ptr();
     let res = f(pdst, psrc, dst.len() as c_ulonglong);
-    (dst.into_iter().skip(bytestodrop).collect(), res)
+    dst.drain(..bytestodrop);
+    (dst, res)
 }