The new setting will allow to host the temporary backup files
into a specific target directory. Defaults to '$CFG->tempdir/backup'.
Calling make_backup_temp_directory() checks that the required sub-directory
will be properly created under the new target directory.
The completion system has code which is supposed to prevent it
updating completion status while grades are being restored. This
code was a nasty hack and had not worked for some time. As a result
completion dates were restored incorrectly.
This commit implements a 'proper' way to find out if a restore is
currently running, replacing the previous hack.
When we import courses or duplicate activities, the deduplicating nature of
the file_storage system means that we don't actually have to include the
real files in the backup - just their metadata from the file table.
The restoration process needs to know not to expect files from the backup
phase so a flag is set in moodle_backup metadata.
