Only complain that files are up-to-date with --force.

Only complain that files are up-to-date with --force.

As a side effect, this also means that when `aclocal' copies the
libtool macros into `aclocal.m4' libtoolize complains only about
the macro files that are missing or not up-to-date.
* libtoolize.m4sh (func_echo_once): New function that prints
the contents of a named variable only on the first call.
(func_aclocal_update_check): New function that compares serial
numbers of libtool macros in aclocal.m4 and only diagnoses the
missing files.
(func_copy, func_copy_cb, func_copy_some_files, func_serial_update)
(func_keyword_update, func_ltmain_update, func_config_update)
(func_install_update): Accept a new argument naming a variable
containing a header string to print with func_echo_once iff any
body text is output by this function.
(func_install_pkgmacro_subproject, func_install_pkgmacro_parent)
(func_install_pkgltdl_files, func_install_pkgconfig_subproject)
(func_install_pkgconfig_parent: Set and pass a suitable
header string variable for the above functions.
(func_serial_update_check): Don't advise rerunning `libtoolize
--force' when aclocal.m4 is not m4_including libtoolize installed
macro files.
* tests/testsuite.at (_LIBTOOLIZE_TRANSFORM): Transform generic
/usr/local/share/aclocal paths to point into the uninstalled
libtool macro directory.
* tests/libtoolize.at: Update tests that were checking for old
behaviour of outputing `file is already up to date' even when
--force was not passed.
* tests/libtoolize.at: New tests to prevent regressions of these
smarter messages.
* NEWS: Updated.
Reported by Olly Betts <olly@survex.com>