ansi2knr: deprecate, it will go away in the next major release

ansi2knr: deprecate, it will go away in the next major release

* doc/automake.texi: Loudly and repeatedly state that the old
de-ANSI-fication features are now deprecated and will be removed
in the next major Automake release.  Other related adjustments.
* lib/Automake/Options.pm (_process_option_list ): Give a warning
in the `obsolete' category when the `ansi2knr' option is used.
* m4/protos.m4 (AM_C_PROTOTYPES): Deprecate this macro: a warning
in the `obsolete' category will be emitted it if is used.
* tests/ansi2knr-deprecation.test: New test.
* tests/Makefile.am (TESTS): Update.
* tests/ansi.test: Adjust, by calling autoconf and/or automake
with the `-Wno-obsolete' flag.
* tests/ansi10.test: Likewise.
* tests/ansi2.test: Likewise.
* tests/ansi3.test: Likewise.
* tests/ansi3b.test: Likewise.
* tests/ansi4.test: Likewise.
* tests/ansi5.test: Likewise.
* tests/ansi6.test: Likewise.
* tests/ansi7.test: Likewise.
* tests/ansi8.test: Likewise.
* tests/ansi9.test: Likewise.
* tests/cxxansi.test: Likewise.
* tests/libobj8.test: Likewise.
* NEWS: Update about the future planned backward-incompatibility
due to the removal of de-ANSI-fication feature.