Use loop-based DFS to resolve rspec#341 (SystemStackError)

lib/rspec/support/source/node.rb

@@ -45,13 +45,18 @@ def location
           @location ||= args.find { |arg| arg.is_a?(Location) }
         end
 
-        def each(&block)
+        def each
           return to_enum(__method__) unless block_given?
 
-          yield self
+          outstanding_nodes = []
+          outstanding_nodes << self
+          while outstanding_nodes.length > 0
+            current_node = outstanding_nodes.pop
+            current_node.children.each do |node|
+              outstanding_nodes.unshift(node)
+            end
 
-          children.each do |child|
-            child.each(&block)
+            yield current_node
           end
         end