Fix fallback if atomic can't be required.

Author: MSch

lib/thread_safe/util/atomic_reference.rb

@@ -8,7 +8,7 @@ module Util
         begin
           require 'atomic'
           defined?(Atomic::InternalReference) ? Atomic::InternalReference : Atomic
-        rescue NameError
+        rescue LoadError,NameError
           require 'thread' # get Mutex on 1.8
           class FullLockingAtomicReference
             def initialize(value = nil)