revlog: move datafile opening in a method
Having file operation centralized into a single spot help to factor common
logic out.
It is also the first step to simplify file handling during batch operation
(eg: revlog cloning). However, that part does not seems to be a hotspot yet.
# 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