Utilize fewer reexports

In regards to:

https://github.com/rust-lang/rust/issues/19253#issuecomment-64836729

This commit:

* Changes the #deriving code so that it generates code that utilizes fewer
  reexports (in particur Option::* and Result::*), which is necessary to
  remove those reexports in the future
* Changes other areas of the codebase so that fewer reexports are utilized

src/libstd/dynamic_lib.rs

@@ -280,7 +280,8 @@ pub mod dl {
     use libc;
     use os;
     use ptr;
-    use result::{Ok, Err, Result};
+    use result::Result;
+    use result::Result::{Ok, Err};
     use slice::SlicePrelude;
     use str::StrPrelude;
     use str;