config: use the new '_unset' value for 'configint'
This should let 'configint' delegates all special processing of the default
config value to the main 'config' method.
# See http://EditorConfig.org for the specificationroot = true[*.py]indent_size = 4indent_style = spacetrim_trailing_whitespace = true[*.{c,h}]indent_size = 8indent_style = tabtrim_trailing_whitespace = true