changelog: fix the diverted opener to accept more kwargs
The current code prevent the use of `atomictemp` file with the changelog
opener. I do not see a good reason for this limitation.
Differential Revision: https://phab.mercurial-scm.org/D7831
# See http://EditorConfig.org for the specification
root = true
[*.py]
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indent_style = space
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[*.{c,h}]
indent_size = 8
indent_style = tab
trim_trailing_whitespace = true
[*.t]
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indent_style = space
trim_trailing_whitespace = false