bash_completion: add -l|--list support for shelve

This was overlooked previously and found via 'hg shelve -p -l <tab>' (to show
the diff of the shelved commit).

contrib/bash_completion

@@ -629,7 +629,7 complete -o bashdefault -o default -o no
 
 _hg_cmd_shelve()
 {
-    if [[ "$prev" = @(-d|--delete) ]]; then
+    if [[ "$prev" = @(-d|--delete|-l|--list) ]]; then
         _hg_shelves
     else
         _hg_status "mard"