Merge branch 'wm/complete-git-short-opts' into jch

The command line completion script (in contrib/) learned to
complete "git -<TAB>" to give single-letter options like "-C".

* wm/complete-git-short-opts:
  completion: complete "git -<TAB>" with short options

contrib/completion/git-completion.bash

@@ -3899,7 +3899,7 @@ __git_main ()
 			;;
 		esac
 		case "$cur" in
-		--*)
+		-*)
 			__gitcomp "
 			--paginate
 			--no-pager
@@ -3915,6 +3915,12 @@ __git_main ()
 			--namespace=
 			--no-replace-objects
 			--help
+			-C
+			-P
+			-c
+			-h
+			-p
+			-v
 			"
 			;;
 		*)