Fixed issue #37
Patch by MorrisR2 has been introduced, but not directly in attendanceregister_get_tracked_users() function, as it would couse side effects: this function is used in many places, not only for retrieving users who need updating in cron.
Merge remote-tracking branch 'origin/issue_37'
fixes issue #36
Renamed 'online' columns that cause reserved word violation on Oracle
Merge remote-tracking branch 'origin/issue_36'
fixes issue #39
overlapping old online sessions were checked  uncorrectly
Merge remote-tracking branch 'origin/issue_39'
fixes issue #36: error on deleting old sessions
fixes issue #41: fixed restore
Merge remote-tracking branch 'origin/issue_36'
Bump version to 2.4.1 (2013012906)
Checked Moodle 2.4 compatibility
Merge remote-tracking branch 'origin/master' into MOODLE_22_STABLE