.editorconfig

ancestors: actually iterate over ancestors in topological order (issue5979)

This code previously used a dequeue logic, the first ancestors seen were the
first ancestors to be emitted. In branching/merging situations, it can result
in ancestors being yielded before their descendants, breaking the object
contract.

We got affected by this issue while working on the copy tracing code. At about
the same time, Axel Hecht <[e-mail]> reported the issue and provided
the test case used in this changeset. Thanks Axel.

Running `hg perfancestors` does not show a significant difference between the
old and the new version.

# 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

[*.t]
indent_size = 2
indent_style = space
trim_trailing_whitespace = false