doc: NEWS: mention the DFA segfault fix

* NEWS (Bug fixes): List the DFA segfault fix.
tests: simplify and factor newest test

* tests/char-class-multibyte2: Simplify file names.
Factor out $e_acute, so that the grep argument representation
is ascii (though the value is still UTF8).
build: update gnulib-related code

* gnulib: Update submodule to latest.
* bootstrap: Update from gnulib.
* gl/lib/regex_internal.h.diff: Update to reflect gnulib changes.
* bootstrap.conf: Partial sync from coreutils.
doc: mention how to use the latest gnulib

* README-hacking: Steal some text from coreutils/README-hacking.