maint: update bug-reporting address

* README: Change bug-gnu-utils@... to bug-diffutils@gnu.org.
* doc/diffutils.texi: Likewise.
Reported by Jamie Landeg Jones.
maint: update copyright year range in texinfo documentation

* doc/diffutils.texi: Update copyright.
gnulib: update to latest, as well as bootstrap
diff: fix performance bug with prefix computation

* src/io.c (find_identical_ends): Fix performance bug:
the test for when the prefix was needed messed up by
the 2002-02-28 integer-overflow fixes, causing performance to be
worse than it needed to be.
diff: fix bug with diff -B and incomplete lines

Reported by Navin Kabra via Eric Blake in:
http://bugs.gnu.org/18402
* src/util.c (analyze_hunk): Don't mishandle incomplete
lines at end of file.
* tests/no-newline-at-eof: Test for the bug.
doc: mention diff -B fix in NEWS