build: update to latest from gnulib

build: update to latest from gnulib

* bootstrap: Update.
* tests/init.sh: Likewise.
* gnulib: Update submodule to latest.

maint: remove two generated files in doc/
* doc/fdl.texi: Remove file from version control.  It is generated.
* doc/gendocs_template: Likewise.
* doc/parted.texi: Add @node ... before inclusion of fdl.texi,
since fdl.texi dropped that part.
* doc/parted-pt_BR.texi: Likewise.
* doc/.gitignore: Update.

build: accommodate newer bootstrap from gnulib
* bootstrap.conf (gnulib_tool_option_extras): Add both --symlink
and --makefile-name=gnulib.mk.  Remove stray use of $bt.
* lib/Makefile.am: Initialize all of the following so that
generated code in gnulib.mk may use += to append to those variables:
AM_CFLAGS, AM_CPPFLAGS, BUILT_SOURCES, CLEANFILES, EXTRA_DIST,
MAINTAINERCLEANFILES, MOSTLYCLEANDIRS, MOSTLYCLEANFILES, SUFFIXES,
noinst_LTLIBRARIES.