Print Libtool project URL in program --help output.

Print Libtool project URL in program --help output.

* configure.ac (AC_INIT): Set PACKAGE argument to `GNU Libtool',
so Autoconf knows this is GNU software.  For Autoconf < 2.64,
if AC_PACKAGE_URL is not defined, substitute PACKAGE_URL.
* Makefile.am (edit): Substitute PACKAGE_URL.
($(srcdir)/tests/package.m4): Also depend on Makefile.am.
Define AT_PACKAGE_URL, for `tests/testsuite --help' output.
* libltdl/config/getopt.m4sh (func_help): Also extract comment
lines that mention a home page and general GNU help.
* libltdl/config/ltmain.m4sh: Use @PACKAGE_BUGREPORT@ instead of
hard-coded list address.  Also mention Libtool home page and
general GNU help web page.
* libtoolize.m4sh: Likewise.

Signed-off-by: Ralf Wildenhues <Ralf.Wildenhues@gmx.de>