My background-erasing changes in r5996/r5997 caused trouble with the

My background-erasing changes in r5996/r5997 caused trouble with the
keyboard-control cursors, and when I tried to fix those more
wallpaper bubbles popped up elsewhere. Here's what I think is a
proper fix: a comprehensive overhaul of the redraw code such that,
instead of tracking the cursor positions explicitly in the
drawstate, we instead track for each peg position whether or not a
cursor is currently displayed at that position. So cursor erasing
and cursor drawing become part of the main draw loop rather than a
separate bit on the end.

[originally from svn r6006]
[r5996 == 3d58feb561ef09cf977f710d69a3562529e23f0f]
[r5997 == a46e3266558eaf5cd18ac2a6322af65c196c3655]