init: warn against obsolete usage of AM_INIT_AUTOMAKE

init: warn against obsolete usage of AM_INIT_AUTOMAKE

Support for the two- and three-arguments invocation forms of the
AM_INIT_AUTOMAKE macro, as in:

  AM_INIT_AUTOMAKE($PACKAGE, $VERSION)

or:

  AM_INIT_AUTOMAKE($PACKAGE, $VERSION, NODEFINE)

will be removed in the next major Automake release (1.13).

Such usages have already been deprecated in the documentation
starting from commit v1.11-2015-ge99690a of 23-02-2012 "docs,
news: document planned removal of obsolete macros and features".

We now start giving runtime warnings as well (in the 'obsolete'
category).

* NEWS: Update.
* m4/init.m4 (AM_INIT_AUTOMAKE): Report the two- and three-arguments
form invocation.
* automake.in (scan_autoconf_traces): Likewise.
* doc/automake.texi: Minor adjustments.  Add an @anchor to the
location where it's described how to modernize outdated invocation
of AM_INIT_AUTOMAKE, so that it can be referenced from automake
warning/error messages.
* t/aminit-moreargs-deprecation.sh: New test.
* tests/list-of-tests.mk: Add it.
* tests/ac-output-old.tap: Adjust by calling automake with the
warnings in the 'obsolete' category disabled.
* t/backcompat.test: Likewise.
* t/backcompat3.test: Likewise.
* t/backcompat5.test: Likewise.
* t/backcompat6.test: Likewise.
* t/version.test: Likewise.
* t/version2.test: Likewise.
* t/pr2.test: Modernize style of AC_INIT and AM_INIT_AUTOMAKE
invocations, and use proper m4 quoting.
* t/pr87.test: Likewise.
* t/confsub.test: Likewise.
* t/install2.test: Likewise.

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