Missed a change needed for Python 2.6 in v0.8
Fixes #174: Fixing singletons for derived classes
Update __str__ to cater for subclasses
Fix for overenthusiastic merging by @robwebset ;)
Merge pull request #175 from robwebset/Python2.6-v0.8

Additional changes needed for Python 2.6 on top of v0.8
Test both if XML element is None AND if .text of that element is None, fixes #181
Merge pull request #183 from KennethNielsen/iss_181_music_lib_parse_fail

Test both if XML element is None AND if .text is None, fixes #181
Fixed typo in SetZoneAttributes