Backup and restore operations should display progress (Backport of MDL-38190)

Progress output for backup and restore operations was added to Moodle 2.6 under MDL-38190.

MDL-38190 is a sub-task of MDL-38189, which has been classified as both a Bug and of Critical priority. The bug is causing timeout problems with our load balancers, as explained in MDL-38190, rendering all backup and restore operations longer than six minutes to be impossible to complete through the UI.

Due to the nature of load balancers playing a role in the situation, this problem is most likely to affect the heaviest users of Moodle (i.e., those who need load balancers). This includes Moodle Partners like us and large educational institutions. We heavy users cannot upgrade to 2.6 immediately upon its release because of non-core code that needs upgrading, training material updates, etc. We also can not wait to fix this critical bug; thus, we need a backport to fix this issue.

In accordance with the backport policy (http://docs.moodle.org/dev/Integration_Review#Backporting), which states that bug fixes will be backported, we are requesting a backport of MDL-38190 to resolve this critical bug prior to 2.6.