musicbrainz/picard — pull request #231 by Sophist-UK (2014-03-06 19:08:13+00:00)
Title: Add %_absolutetracknumber% variable...

...so you can number tracks sequentially on multi-track discs without
using a disc number.

See http://forums.musicbrainz.org/viewtopic.php?pid=25326 for
requirement.