Always try to update the version when autogen.sh is run

This avoids at least one case where ./autogen.sh && ./configure && make
will re-run configure because the makefile rules updated something that
it depends upon. Pulling a new version from git will change the version
so we should update that at the first step rather than iterating after
the last one.

configure.ac

@@ -4,7 +4,8 @@ dnl The package_version file will be automatically synced to the git revision
 dnl by the update_version script when configured in the repository, but will
 dnl remain constant in tarball releases unless it is manually edited.
 m4_define([CURRENT_VERSION],
-          m4_esyscmd([ if test -e package_version || ./update_version; then
+          m4_esyscmd([ ./update_version 2>/dev/null || true
+                       if test -e package_version; then
                            . ./package_version
                            printf "$PACKAGE_VERSION"
                        else