completion: reflog subcommands and options

Make generic the completion for reflog subcommands and its options.

Note that we still need to special case the options for "show".

Signed-off-by: Rubén Justo <rjusto@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

contrib/completion/git-completion.bash

@@ -2445,8 +2445,12 @@ _git_rebase ()
 
 _git_reflog ()
 {
-	local subcommands="show delete expire"
-	local subcommand="$(__git_find_subcommand "$subcommands" "show")"
+	local subcommands subcommand
+
+	__git_resolve_builtins "reflog"
+
+	subcommands="$___git_resolved_builtins"
+	subcommand="$(__git_find_subcommand "$subcommands" "show")"
 
 	case "$subcommand,$cur" in
 	show,--*)
@@ -2455,6 +2459,10 @@ _git_reflog ()
 			"
 		return
 		;;
+	$subcommand,--*)
+		__gitcomp_builtin "reflog_$subcommand"
+		return
+		;;
 	esac
 
 	__git_complete_refs