zoom and pan suck

[norill]

3 issues here:

• point under cursor should not move during zooming. right now its impossible to just zoom in, because the screen would also pan and you end up with empty space on screen.
• zooming should not add dozens of entries to undo/redo history. i don't think it should add entries at all.
• there is no reason to require users to hold shift to zoom.

[pkundrat]

although the zoom should not go to undo history - it might be really nice to have a separate zoom history - and move ahead/backwords freely