Incomplete MusicXML text attributes for 7sus4 chords

2.0, Ubuntu 14.04

As per discussions in http://musescore.org/en/node/51321 and http://forums.makemusic.com/viewtopic.php?f=12&t=2899, it seems that some applications will need additional help in constructing appropriate text representations for chord symbols. In particular, 7sus4 (and 9sus4, 11sus4, and 13sus4). What we export now is not incorrect, and we actually can import it just fine ourselves, but other applications will have trouble with it. Michael Good recommends we munge the text attribute on the kind tag to make the desired spelling more explicit.

I have code to do this, just need to do more testing, and am also awaiting clarifaction on a couple of other points to see if other related changes are warranted.