Add support for an Autotest test suite for Bison.

* m4/m4.m4, m4/atconfig.m4: New files.
* m4/Makefile.am (EXTRA_DIST): Adjust.
* tests/suite.m4, tests/Makefile.am, tests/atgeneral.m4: New
files.
* src/getargs.c: Display a more standard --version message.
* src/reader.c (reader): Formatting changes.
No longer depend upon VERSION_STRING.
* configure.in: No longer use `dnl'.
Set up the test suite and the new directory `tests/.
(VERSION_STRING): Remove.

m4/Makefile.am

@@ -1,3 +1,10 @@
 ## Process this file with automake to produce Makefile.in -*-Makefile-*-
-EXTRA_DIST = bison-decl.m4 error.m4 gettext.m4 lcmessage.m4 progtest.m4 \
-             warning.m4
+EXTRA_DIST = \
+atconfig.m4 \
+bison-decl.m4 \
+error.m4 \
+gettext.m4 \
+lcmessage.m4 \
+m4.m4 \
+progtest.m4 \
+warning.m4