Mouse-over effects in Factor Histogram can be activated while dragging parameter tabs

[Vectornaut]

I think the histogram bars' mouse-over effects should always be inactive when you're dragging a parameter tab. The current interface deviates from this in at least two cases.

Drag-first case

1. View a Factor Histogram visualization.
2. Undock one parameter tab.
3. In the process of undocking the other parameter tab, move the cursor over a few histogram bars.
   • Actual behavior: The histogram bars' mouse-over effects activate
   • Expected behavior: The histogram bars' mouse-over effects don't activate

Mouse-over-first case

1. View a Factor Histogram visualization.
2. Undock a parameter tab and drop it in a place where its title bar partially covers a histogram bar.
3. Mouse over the rectangle where the title bar and the histogram bar intersect
   • The histogram bar's mouse-over effect activates
4. Click and drag the parameter tab.
   • Actual behavior: The histogram bar's mouse-over effect stays active
   • Expected behavior: The histogram bar's mouse-over effect deactivates when you click, and no other mouse-over effects activate while you drag

[gwhitney]

Fixed in ui2 by #568, closing.