MFC 238423,238426,238428,258063,258063,258066,258097,258185,259134:

MFC 238423,238426,238428,258063,258063,258066,258097,258185,259134:
The etcupdate utility is a tool for managing updates to files that are
not updated as part of `make installworld' such as files in /etc.  It
manages updates by doing a three-way merge of changes made to these files
against the local versions.  It is also designed to minimize the amount
of user intervention with the goal of simplifying upgrades for clusters
of machines.

git-svn-id: svn://svn.freebsd.org/base/stable/9@260650 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f