This more clearly distingiushes pre-April-7 ChangeLog entries (which
are for top-level files only) from post-April-7 entries (which are
about files at all levels. Problem reported by Glenn Morris in:
http://lists.gnu.org/archive/html/emacs-devel/2015-04/msg00678.html
* ChangeLog.1: Move post-April-7 entries from here ...
* ChangeLog.2: ... to this new file.
* Makefile.in (CHANGELOG_HISTORY_INDEX_MAX): Bump to 2.