Fix subclasses not inheriting headers set in the superclass

The implementation of InheritedHash worked fine when look up individual keys, but when
it was merged into the request headers inside the Connection class, it didn't consider
the @parent_hash.

Author: meanphil

lib/active_resource/connection.rb

@@ -211,7 +211,7 @@ def default_header
 
       # Builds headers for request to remote service.
       def build_request_headers(headers, http_method, uri)
-        authorization_header(http_method, uri).update(default_header).update(http_format_header(http_method)).update(headers)
+        authorization_header(http_method, uri).update(default_header).update(http_format_header(http_method)).update(headers.to_hash)
       end
 
       def response_auth_header

lib/active_resource/inheriting_hash.rb

@@ -11,5 +11,24 @@ def initialize(parent_hash = {})
     def [](key)
       super || @parent_hash[key]
     end
+
+    # Merges the flattened parent hash (if it's an InheritingHash)
+    # with ourself
+    def to_hash
+       @parent_hash.to_hash.merge(self)
+    end
+    
+    # So we can see the merged object in IRB or the Rails console
+    def pretty_print(pp)
+      pp.pp_hash to_hash
+    end  
+
+    def inspect
+      to_hash.inspect
+    end
+
+    def to_s
+      inspect
+    end
   end
 end