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/m4.m4

@@ -0,0 +1,14 @@
+# serial 1
+
+# BISON_AC_PROG_GNU_M4
+# --------------------
+# Check for GNU m4, at least 1.3 (supports frozen files).
+AC_DEFUN([BISON_AC_PROG_GNU_M4],
+[AC_PATH_PROGS(M4, gm4 gnum4 m4, m4)
+AC_CACHE_CHECK(whether m4 supports frozen files, ac_cv_prog_gnu_m4,
+[ac_cv_prog_gnu_m4=no
+if test x"$M4" != x; then
+  case `$M4 --help < /dev/null 2>&1` in
+    *reload-state*) ac_cv_prog_gnu_m4=yes ;;
+  esac
+fi])])