I'm sorely tempted to move LRUCache to Balloon. It's in System at the
moment, making Balloon depend on System.

Doing so would make Balloon not depend on System anymore. The other
user of LRUCache is ScrollBar, which is in Morphic. Morphic already
depends on Balloon, so nothing happens.

In short: this
* moves LRUCache closer to one of its two users
* breaks a needless dependency

Thoughts?

frank