[Source::Lock] Avoid hash collisions with un-wrapped sources

lib/rubygems/source/lock.rb

@@ -34,6 +34,10 @@ def == other # :nodoc:
     0 == (self <=> other)
   end
 
+  def hash # :nodoc:
+    @wrapped.hash ^ 3
+  end
+
   ##
   # Delegates to the wrapped source's fetch_spec method.
 
@@ -46,4 +50,3 @@ def uri # :nodoc:
   end
 
 end
-