Changed error message if inspect command is called.

If the webinspector isn't enabled the error messaged showed the webkit setting
that is not set to use the webinspector. But this setting has an alias and can
therefore only be set by the alias. So we print the alias in the error
message.
Changed url_history_get_all to add the entries to existing given list.

This will allow us to combine url history and later to implement bookmarks in
a single completion list.