#127539: progressive operation support, refactoring update.php code to a...

#127539: progressive operation support, refactoring update.php code to a generic batch API to support runnning operations in multiple HTTP requests
  - update.php is already on the batch API
  - node access rebuilding is in the works
  - automatic locale importing is in the works

 Thanks to Yves Chedemois (yched) for the good code quality, very wide awareness of issues related to batches,
 and the fantastic turnaround times. Hats off.