silent-rules reorganization, --enable-silent-rules switch.

silent-rules reorganization, --enable-silent-rules switch.

This patch introduces a configure-time option to set the default
verbosity.  Since configure now needs to know whether the
`silent-rules' automake option was set, the latter can only be
set within AM_INIT_AUTOMAKE, or with a new AM_SILENT_RULES macro
but not any more through AUTOMAKE_OPTIONS or the automake
command line option `--silent-rules'.

* automake.in (define_verbose_var): Define the default verbose
variable in terms of `$(AM_DEFAULT_VERBOSITY)'.
(handle_configure): Do not pass `--silent-rules' to automake.
(scan_autoconf_traces): Trace `AM_SILENT_RULES'.  If seen,
enable global `silent-rules' option.
(usage): Do not document `--silent-rules'.
(parse_arguments): Do not accept `--silent-rules'.
* doc/automake.texi (Options): Overhaul.  Document
AM_SILENT_RULES, --enable-silent-rules, --disable-silent-rules,
AM_DEFAULT_VERBOSITY.  Show an example for user-added variables
for less verbose output.
(Invoking Automake): Remove documentation for `--silent-rules'.
(Public Macros): Document `AM_SILENT_RULES'.
* NEWS: Update.
* lib/Automake/Options.pm (_process_option_list): Accept
`silent-rules' only as option in configure.ac.
* m4/init.m4 (AM_INIT_AUTOMAKE): If the `silent-rules' option
was enabled, require `AM_SILENT_RULES'; move AM_BACKSLASH
initialization to ...
* m4/silent.m4 (AM_SILENT_RULES): ... this new file, new macro.
Deal with `--enable-silent-rules' switch; define
AM_DEFAULT_VERBOSITY.
* m4/Makefile.am (dist_m4data_DATA): Add silent.m4.
* tests/dollarvar.test: Remove tests for `--silent-rules', use
`AM_SILENT_RULES'.
* tests/flavor.test: Remove test for `--silent-rules'.
* tests/silent.test: Use `AM_SILENT_RULES' instead of
`AUTOMAKE_OPTIONS = silent-rules'; use `--enable-silent-rules'.
* tests/silent2.test: Likewise.
* tests/silent3.test: Likewise.
* tests/silent4.test: Likewise.
* tests/silent5.test: Likewise.
* tests/silent6.test: Likewise. Test `AM_SILENT_RULES' as well
as `AM_INIT_AUTOMAKE([silent-rules])' instead of
`--silent-rules'.
* tests/silent7.test: Use `AM_SILENT_RULES' instead of
`AUTOMAKE_OPTIONS = silent-rules'; ensure the latter is rejected.
Test combinations of --enable-silent-rules and
--disable-silent-rules with `make V=0' and `make V=1'.
Suggestion for configure-time switch by Bob Friesenhahn.

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