Improve autogen.sh.

Makefile.am

@@ -2,6 +2,8 @@
 
 ACLOCAL_AMFLAGS = -I m4
 
+AUTOMAKE_OPTIONS = foreign
+
 SUBDIRS = src
 
 EXTRA_DIST =                                                                 \

autogen.sh

@@ -15,13 +15,8 @@ fi
 
 set -ex
 
-rm -rf autom4te.cache
-
-aclocal-1.9 --force -I m4
-libtoolize -c -f
-autoheader -f -W all
-automake-1.9 --foreign -a -c -f -W all
-autoconf -f -W all,no-obsolete
+# TODO(kenton):  Use -Wall and fix the resulting warnings.
+autoreconf -f -i
 
 rm -rf autom4te.cache config.h.in~
 exit 0