Merge branch 'cn/branch-set-upstream-to'

Finishing touches to the recently graduated topic to introduce
"git branch --set-upstream-to" option.

* cn/branch-set-upstream-to:
  completion: complete branch name for "branch --set-upstream-to="
  completion: add --set-upstream-to and --unset-upstream

contrib/completion/git-completion.bash

@@ -875,11 +875,15 @@ _git_branch ()
 	done
 
 	case "$cur" in
+	--set-upstream-to=*)
+		__gitcomp "$(__git_refs)" "" "${cur##--set-upstream-to=}"
+		;;
 	--*)
 		__gitcomp "
 			--color --no-color --verbose --abbrev= --no-abbrev
 			--track --no-track --contains --merged --no-merged
-			--set-upstream --edit-description --list
+			--set-upstream-to= --edit-description --list
+			--unset-upstream
 			"
 		;;
 	*)