r=nathan

build-core's HEAD is going to diverge for 1.6.0, so "capture" build-core's
current state in a branch mainly for b1_4.
Note that b_release_1_4_6-patchless is not really a release branch and thus
tracks b1_4.
Also, v1_2_8 and v1_4_0 pre-existed this build system so which branch to
check out for them is actually quite moot.  Let's just keep them tracking
b1_4.

lustrecvs

@@ -57,10 +57,12 @@ case "$lustretag" in
     # These releases did not get build tagged for them because they
     # this build system didn't exist when they were tagged
     v1_2_8|v1_4_0) 
-        buildtag="HEAD"
+        buildtag="b1_4"
         ;;
     
-    b_release_1_4_6-patchless) buildtag="HEAD" ;;
+    b1_4*) buildtag="b1_4" ;;
+
+    b_release_1_4_6-patchless) buildtag="b1_4" ;;
 
     v* | b_release*) buildtag=$lustretag ;;