AdiumTabStyle: adjust the icon in vertical tabs when the indicator is shown.
AdiumTabStyle: scale the large image to fit the forced width.
Also fix its vertical centring.
AdiumTabStyle: fix the title overlapping the icon.
Cleaned up -titleRectForBounds's variables that were used in both horizontal and vertical calculations.
Prevent creating invisible windows. If a single-tab window's tab is dragged onto itself, it'll disappear from view because the window it dragged from is hidden.