Pull in recent maintainer improvements from coreutils.

Pull in recent maintainer improvements from coreutils.

* GNUmakefile (_is-dist-target): 'make distclean' should not
trigger autoreconf.
(_dummy): Change directories before removing autom4te.cache.
(check dist distcheck install) [!_have-Makefile]: Provide nicer
diagnostics.
* configure.ac (AC_CONFIG_LINKS): Copy GNUmakefile into VPATH
builds, after initial bootstrap.
* Makefile.am (distclean-local): Work around current automake bug.
* Makefile.maint (ME): Allow VPATH usage.

Signed-off-by: Eric Blake <ebb9@byu.net>