check: enable gnulib's testsuite

check: enable gnulib's testsuite

* Makefile.am (SUBDIRS): Add gnulib-tests.
(EXTRA_DIST): Distribute also update-copyright script.  This does
not happen automatically because we manually remove ./lib
directory created by gnulib-tool.  Not having the file distributed
causes 'make check' failure, however.
(dotversion): Fix to point to $(top_srcdir).
* bootstrap.conf (gnulib_tool_options): Add gnulib-tool args
needed to successfully install gnulib's tests.
* configure.ac (CONFIG_STATUS_DEPENDENCIES): Look for .version in
$(top_srcdir).
* gnulib: Sync with upstream.
* build-aux/.gitignore: Ignore ar-lib coming from automake.