maint: avoid new syntax-check failure re @xref

* doc/parted.texi: Adjust @xref usage: it must be used only
at start of sentence.
* doc/parted-pt_BR.texi: Likewise.
maint: don't prohibit strncpy just yet

* cfg.mk (local-checks-to-skip): Add sc_prohibit_strncpy,
so that we do not yet enable the strncpy prohibition.
There are many uses, and it will be a lot of work to remove
all of them.
build: update gnulib, bootstrap and init.sh
build: prefer $(AM_CPPFLAGS) over $(INCLUDES)

The latter is obsolete, and might be removed in future Automake versions.
Moreover, it's already been removed in Automake-NG, so its use would make
a port to Automake-NG more difficult.

* parted/Makefile.am (INCLUDES): Rename ...
(AM_CPPFLAGS): ... like this.
* partprobe/Makefile.am: Likewise.
* libparted/fs/Makefile.am: Likewise.
* libparted/Makefile.am: Likewise.
* libparted/labels/Makefile.am: Likewise.

Copyright-paperwork-exempt: yes
build: don't list files with unknown suffix in _SOURCES

While this works with mainline Automake (which blindly treats source
files with an unknown extension as if they were header files), it is
undocumented (albeit admittedly unlikely to change).  Moreover, it no
longer works with Automake-NG (and that's by design), so the use of
such feature would make a port to Automake-NG more difficult.

* libparted/labels/Makefile.am (liblabels_la_SOURCES): ... don't
list 'pt-limit.gperf' here; rather ...
(EXTRA_DIST): ... list 'pt-limit.c' and 'pt-limit.gperf' here.
(EXTRA_DIST, BUILT_SOURCES): Enhance few comments.

Copyright-paperwork-exempt: yes
build: prefer pattern rules over suffix rules

That is acceptable, because the GNU parted build system already
requires GNU make anyway: the $(subst ...) built-in is used in the
common recipe for the 'ss-1024', 'ss-2048' and 'ss-4096' targets
in Makefile.am.

* include/parted/Makefile.am (.in.h.h): Rename ...
(%.h: %.in.h): ... as this pattern rule.
(SUFFIXES): Delete, no more needed.

Copyright-paperwork-exempt: yes
build: enable subdir-objects Automake option globally

That option is enabled unconditionally in Automake-NG, and enabling
it also for mainline Automake will help to ensure no unexpected
incompatibilities is introduced in a potential port to Automake-NG.

Moreover, if we have a source file 'sub/foo.c', having it compiled
in 'sub/foo.o' rather than in 'foo.o' is undeniably cleaner and more
natural.

* configure.ac (AM_INIT_AUTOMAKE): Add 'subdir-objects'.
* libparted/fs/Makefile.am (AUTOMAKE_OPTIONS): No need to declare
'subdir-objects' explicitly now.

Copyright-paperwork-exempt: yes
tests: prefer AM_TESTS_ENVIRONMENT over TESTS_ENVIRONMENT

The latter should be reserved for user overrides.

* tests/Makefile.am (TESTS_ENVIRONMENT): Rename ...
(AM_TESTS_ENVIRONMENT): ... like this.

Copyright-paperwork-exempt: yes
tests: remove unused AM_TESTS_ENVIRONMENT entries

Probably a copy&paste errors, likely from the TESTS_ENVIRONMENT
definition in the 'tests/Makefile.am' in GNU coreutils.

* tests/Makefile.am (AM_TESTS_ENVIRONMENT): Don't define nor export
any of the variables PREFERABLY_POSIX_SHELL, REPLACE_GETCWD, CC,
MAKE, PERL.

Copyright-paperwork-exempt: yes
build: require Automake >= 1.11.6

Now that we use AM_TESTS_ENVIRONMENT, we should require at least
Automake >= 1.11.2; but since all the Automake version until 1.11.5
are vulnerable to CVE-2012-3386:

    <https://lists.gnu.org/archive/html/automake/2012-07/msg00023.html>

it's even better to require 1.11.6.

* configure.ac (AM_INIT_AUTOMAKE): Bump version requirement to 1.11.6.
* bootstrap.conf ($buildreq): Likewise.

Copyright-paperwork-exempt: yes
maint: make Autoconf version requirement consistent

* bootstrap.conf ($buildreq): Require Autoconf >= 2.63, not >= 2.61,
for consistency with what is done in AC_INIT in configure.ac

Copyright-paperwork-exempt: yes
maint: tighten per version requirement

* bootstrap.conf ($buildreq): Require Perl >= 5.6 (not merely >= 5.5),
because that's the minimal version required by modern Automake and
Autoconf.

Copyright-paperwork-exempt: yes
build: support (and require) Automake-NG

* configure.ac (AC_PREREQ): Require Autoconf version >= 2.65,
since that is the minimal version supported by Automake-NG.
(AM_INIT_AUTOMAKE): Add the 'ng' option, to ensure that mainstream
Automake is not used by mistake when bootstrapping.  Don't add the
'parallel-tests', 'subdir-objects' nor 'color-tests' options, since
those are on by default with Automake-NG.  Don't add the "minimal
required version", since Automake-NG is still in alpha state, and
is version is something like '1.12a' at the moment of writing.
Also, drop the 'dist-xz' and 'no-dist-gzip' options; they are not
supported anymore, and the same effect is now obtained ...
* Makefile.am (AM_DIST_FORMATS): ... defining this to 'xz'.
* bootstrap.conf ($buildreq): Require 'automake-ng' and
'aclocal-ng'; no longer require mainstream 'automake'.
Bump required 'autoconf' version to 2.65.
* m4/mkdirp-compat.m4: New file, contain a definition of the macro
'AM_PROG_MKDIR_P' (simply as an alias to the Autoconf-provided
macro 'AC_PROG_MKDIR_P'), that is used by the Gettext-provided
macro 'AM_PO_SUBDIRS', but which has been removed in Automake-NG
(as well as in the master branch of mainline Automake).
* .gitignore: Don't ignore 'm4/mkdirp-compat.m4'.  Ignore '.am/'
directories used internally by Automake-NG generated recipes.

Signed-off-by: Stefano Lattarini <stefano.lattarini@gmail.com>