Don't handle command and :open history different.

Don't handle command and :open history different.

The stepping through history via <up> and <down> keys generated different
items for ':open<up>' and ':open <up>'. The reason for this was that we looked
up the history file to get the item, ':open<up>' entries where collected from
command history file where also none url entries are available (like call with
shortcuts).

Now the history lookup does not distinguish between commands and urls and
follows the inspiring example of vim, where ':e <up>' also lists none
processed values like ':e %'.