mdiff: add a config option to use xdiff algorithm The `experimental.xdiff` will affect the default diffopts and make mdiff use the xdiff algorithm for better diff quality. Differential Revision: https://phab.mercurial-scm.org/D2603

# 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