merge: use labels in subrepo merge
This is the last place that doesn't respect conflict labels in merge output.
Teach subrepos to use subrepo merge output too.
# 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