bash: not all 'git bisect' subcommands make sense when not bisecting

... but only 'start' and 'replay'.  The other commands will either
error out or offer to start bisecting for the user.

Signed-off-by: SZEDER Gábor <szeder@ira.uka.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/contrib/completion/git-completion.bash b/contrib/completion/git-completion.bash
index 5e023d4..d739113 100755
--- a/contrib/completion/git-completion.bash
+++ b/contrib/completion/git-completion.bash
@@ -907,7 +907,11 @@
 	local subcommands="start bad good skip reset visualize replay log run"
 	local subcommand="$(__git_find_on_cmdline "$subcommands")"
 	if [ -z "$subcommand" ]; then
-		__gitcomp "$subcommands"
+		if [ -f "$(__gitdir)"/BISECT_START ]; then
+			__gitcomp "$subcommands"
+		else
+			__gitcomp "replay start"
+		fi
 		return
 	fi