Fixed value bug in the tooltip hook: If a scan had not been performed, skill level data for the given profession would be a boolean instead of a number - now this is treated as 0 skill.

Fixed value bug in the tooltip hook: If a scan had not been performed, skill level data for the given profession would be a boolean instead of a number - now this is treated as 0 skill.
In addon:Scan(): Added an is_refresh parameter and some state-saving/comparison for number of recipes known. This ensures that we only refresh the displayed list when a new recipe is learned. Previously, this was occurring every time TRADE_SKILL_UPDATE was fired, which appears to have the ability to be broadcast from other players.