rhg: allow setting defaults.cmd to an empty string
This is used by at least one hg UI to prevent defaults from affecting
the command:
https://github.com/emacs-mirror/emacs/blob/b71beb7ae7c60a5c5af608420d28fdda5265a264/lisp/vc/vc-hg.el#L245
Let's let it work.
# See http://EditorConfig.org for the specification
root = true
[*.py]
indent_size = 4
indent_style = space
trim_trailing_whitespace = true
end_of_line = lf
[*.{c,h}]
indent_size = 8
indent_style = tab
trim_trailing_whitespace = true
end_of_line = lf
[*.t]
indent_size = 2
indent_style = space
trim_trailing_whitespace = false
end_of_line = lf