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/libcoretest/num/mod.rs

@@ -48,7 +48,8 @@ pub fn test_num<T>(ten: T, two: T) where
 
 #[cfg(test)]
 mod test {
-    use core::option::{Option, Some, None};
+    use core::option::Option;
+    use core::option::Option::{Some, None};
     use core::num::Float;
     use core::num::from_str_radix;