PatronAdapter should use Session#default_response_charset.

lib/webmock/http_lib_adapters/patron_adapter.rb

@@ -25,7 +25,7 @@ def handle_request_with_webmock(req)
               WebMock::HttpLibAdapters::PatronAdapter.
                 handle_file_name(req, webmock_response)
               res = WebMock::HttpLibAdapters::PatronAdapter.
-                build_patron_response(webmock_response)
+                build_patron_response(webmock_response, default_response_charset)
               WebMock::CallbackRegistry.invoke_callbacks(
                 {:lib => :patron}, request_signature, webmock_response)
               res
@@ -98,10 +98,10 @@ def self.build_request_signature(req)
           request_signature
         end
 
-        def self.build_patron_response(webmock_response)
+        def self.build_patron_response(webmock_response, default_response_charset)
           raise ::Patron::TimeoutError if webmock_response.should_timeout
           webmock_response.raise_error_if_any
-          
+
           header_fields = (webmock_response.headers || []).map { |(k, vs)| Array(vs).map { |v| "#{k}: #{v}" } }.flatten
           status_line   = "HTTP/1.1 #{webmock_response.status[0]} #{webmock_response.status[1]}"
           header_data   = ([status_line] + header_fields).join("\r\n")
@@ -111,7 +111,8 @@ def self.build_patron_response(webmock_response)
             webmock_response.status[0],
             0,
             header_data,
-            webmock_response.body
+            webmock_response.body,
+            default_response_charset
           )
         end