Add companion-module core.rs that exports log levels and option/some/none everywhere.

src/test/run-pass/alt-bot.rs

@@ -1,5 +1,3 @@
-use std;
-import option::*;
 
 fn main() {
     let i: int =

src/test/run-pass/check-pattern-bound.rs

@@ -1,5 +1,4 @@
 use std;
-import option::*;
 
 pure fn p(x: int) -> bool { true }
 

src/test/run-pass/nested-alts.rs

@@ -1,7 +1,4 @@
 
-use std;
-import option::*;
-
 fn baz() -> ! { fail; }
 
 fn foo() {

src/test/run-pass/pattern-bound-var-in-for-each.rs

@@ -1,13 +1,9 @@
 // Tests that trans_path checks whether a
 // pattern-bound var is an upvar (when translating
 // the for-each body)
-use std;
-import option::*;
-import uint;
 
 fn foo(src: uint) {
 
-
     alt some(src) {
       some(src_id) {
         uint::range(0u, 10u) {|i|