Fix two small warnings

src/libextra/uuid.rs

@@ -787,7 +787,7 @@ mod bench {
     pub fn parse_str(bh: &mut BenchHarness) {
         let s = "urn:uuid:F9168C5E-CEB2-4faa-B6BF-329BF39FA1E4";
         do bh.iter {
-            let u = Uuid::parse_string(s);
+            Uuid::parse_string(s);
         }
     }
 }

src/libstd/run.rs

@@ -949,7 +949,7 @@ fn waitpid(pid: pid_t) -> int {
 #[cfg(test)]
 mod tests {
     use io;
-    use libc::{c_int, uintptr_t};
+    use libc::c_int;
     use option::{Option, None, Some};
     use os;
     use path::Path;