Branch b1_6

Increase build version to 1.6.4.52 for new tag.

lustre/autoconf/lustre-version.ac

 m4_define([LUSTRE_MAJOR],[1])
 m4_define([LUSTRE_MINOR],[6])
 m4_define([LUSTRE_PATCH],[4])
-m4_define([LUSTRE_FIX],[51])
+m4_define([LUSTRE_FIX],[52])
 # Note: we're starting prerelease versions at 50 this time.
 
 dnl # liblustre delta is 0.0.1.32 , next version with fixes is ok, but