ENH: only set ParaView_MAJOR by default if not already set

etc/apps/paraview3/bashrc

@@ -62,7 +62,7 @@ case "$ParaView_VERSION" in
     ;;
 
 *)
-    ParaView_MAJOR=`echo $ParaView_VERSION | sed -e 's/^\([0-9][0-9]*\.[0-9][0-9]*\).*$/\1/'`
+    [ -z ${ParaView_MAJOR} ] && ParaView_MAJOR=`echo $ParaView_VERSION | sed -e 's/^\([0-9][0-9]*\.[0-9][0-9]*\).*$/\1/'`
     ;;
 esac
 export ParaView_MAJOR