use gnulib's "open" module

* bootstrap.conf (gnulib_modules): Add open.
This is required at least for Solaris 9 and HP-UX 11, to
avoid a truncate test failure.  For details, see this thread:
http://thread.gmane.org/gmane.comp.gnu.coreutils.bugs/13755

bootstrap.conf

@@ -105,6 +105,10 @@ gnulib_modules="
 	xstrtol xstrtold xstrtoumax yesno
 "
 
+# Required at least for truncate's truncate-fail-diag test
+# on Solaris 7, Solaris 9, and HP-UX 11.
+gnulib_modules="$gnulib_modules open"
+
 # Other locale categories that need message catalogs.
 EXTRA_LOCALE_CATEGORIES=LC_TIME