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/libcore/num/mod.rs

@@ -30,7 +30,8 @@ use kinds::Copy;
 use mem::size_of;
 use ops::{Add, Sub, Mul, Div, Rem, Neg};
 use ops::{Not, BitAnd, BitOr, BitXor, Shl, Shr};
-use option::{Option, Some, None};
+use option::Option;
+use option::Option::{Some, None};
 use str::{FromStr, from_str, StrPrelude};
 
 /// Simultaneous division and remainder