Updated build version

lustre/autoconf/lustre-version.ac

 m4_define([LUSTRE_MAJOR],[1])
 m4_define([LUSTRE_MINOR],[6])
 m4_define([LUSTRE_PATCH],[0])
-m4_define([LUSTRE_FIX],[90])
+m4_define([LUSTRE_FIX],[91])
 
 dnl # liblustre delta is 0.0.1.32 , next version with fixes is ok, but
 dnl # after following release candidate/beta would spill this warning already.