[transaction] move RQLRewriter in Transaction
This remove the last ``AttributeError`` magic. The ``RQLRewriter`` needs a Session. Its
reset is handled in ``Session`` code to handle that
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))