Don't add duplicate query to history

Moved from GitHub ratel/77

Posted by codexnull:

I guess looking at the query history can tell you how many times you’ve run a particular query, but I would find it more useful to show more queries I can easily re-run instead.

I think it would be better if a query was not added to the history panel if it is the same the last entry. Or even better, a query is not added to the history if it is the same as a query already shown in the history panel. This would give the user more unique queries to easily recall.