tests/test-gendoc-zh_CN.t

config: use the new '_unset' value for 'configbool'

This should let 'configbool' delegate all special processing of the default
config value to the main 'config' method.

The default value for bool (False) is still enforced in this method if no other
default were passed.

#require docutils gettext

  $ $TESTDIR/check-gendoc zh_CN
  checking for parse errors