TCON parsing fixes

 * Don't join multiple 2.4 TCON fields together
 * Don't add duplicate fields for 2.3 genres where the refinement matches the ID3v1 genre

Patch by Michael Smith
BUG:188578


git-svn-id: svn://anonsvn.kde.org/home/kde/trunk/kdesupport/taglib@994805 283d02a7-25f6-0310-bc7c-ecb5cbfe19da