changelogs merged in gnulib

[Paul Eggert]

I merged all the gnulib ChangeLog files into one ChangeLog, at the
top.  The merge was mostly done automatically, and no doubt could be
done better (i.e., related changes put together), but that can be done
later if someone has the time.

The changes are long and mechanical, so I'm not including them here.
Here's a URL if you want to see them:

http://cvs.savannah.gnu.org/viewcvs/gnulib/ChangeLog?root=gnulib&r1=1.718&r2=1.719