[data] Use correct syntax to unset CSS attributes (closes #8602446) 'default' is actually a recognized CSS cursor name (the regular pointer). Using this value doesn't revert to whatever cursor DOM elements have by default ('pointer' on links, 'text' on text, etc). The proper way to unset a CSS attribute on DOM elements is to set it to an empty string. http://stackoverflow.com/questions/2027935/how-to-remove-css-property-using-javascript

import ConfigParser
try:
    undo_actions = config.cfgfile_parser.get('MAIN', 'undo-support', False)
except ConfigParser.NoOptionError:
    pass # this conf. file was probably already migrated
else:
    config.global_set_option('undo-enabled', bool(undo_actions))