sum: New (generic long option) completion (RedHat: #717341).

bash_completion

@@ -1696,7 +1696,7 @@ for i in a2ps awk bash bc bison cat colordiff cp csplit \
     curl cut date df diff dir du enscript env expand fmt fold gperf gprof \
     grep grub head indent irb ld ldd less ln ls m4 md5sum mkdir mkfifo mknod \
     mv netstat nl nm objcopy objdump od paste patch pr ptx readelf rm rmdir \
-    sed seq sha{,1,224,256,384,512}sum shar sort split strip tac tail tee \
+    sed seq sha{,1,224,256,384,512}sum shar sort split strip sum tac tail tee \
     texindex touch tr uname unexpand uniq units vdir wc wget who; do
     have $i && complete -F _longopt -o default $i
 done