Cappuccino Cappuccino

Refs #1559. Autosave split view positions for frame size changes.

This covers the case where the whole split view is resized and the divider moves as a consequence. For example if the split view was made much smaller the fixed position of the divider previously autosaved might not even be inside of the split view frame anymore, and on restore from autosave that side of the split view might unexpectedly become collapsed.

The new behaviour also more closely matches Cocoa's, although there is still a slight difference in implementation.
https://github.com/cappuccino/cappuccino/commit/c9b7d1e8424248a9531...