libgit2/libgit2 — pull request #1838 by carlosmn (2013-09-07 22:57:23+00:00)
Title: revwalk: allow simplifying by first-parent

When enabled, only the first parent of each commit will be queued,
enabling a simple way of using first-parent simplification.

This is the simplest of the history simplification options. This one doesn't involve any parent rewriting, so we can use the existing `git_revwalk_next()`.