cmdutil: extract a _changesetlabels function out of changeset_printer._show()
There is a common logic in changeset_printer and in the summary command for
labelling a changeset.
This prepares extension of changeset's labels with evolution "troubles"
information that would show up in both log and summary outputs. Ultimately,
both would use this function.
# See http://EditorConfig.org for the specification
root = true
[*.py]
indent_size = 4
indent_style = space
trim_trailing_whitespace = true
[*.{c,h}]
indent_size = 8
indent_style = tab
trim_trailing_whitespace = true