#629794 by yched: Fix Scaling issues with batch API. (with tests)

includes/batch.inc

includes/batch.queue.inc

includes/form.inc

includes/update.inc

modules/simpletest/tests/batch.test

modules/simpletest/tests/batch_test.callbacks.inc

modules/simpletest/tests/batch_test.info

modules/simpletest/tests/batch_test.module

modules/simpletest/tests/form.test

modules/simpletest/tests/form_test.module

modules/simpletest/tests/system_test.module

modules/system/system.install

modules/system/system.module

modules/system/system.queue.inc