Fix SC.SegmentedView crash.

Encountered a situation where adjustOverflow was being called in between
itemsDidChange and remeasure. This meant that cachedDims hadn't been
updated yet. In this case, just return and let the scheduled remeasure take
care of it.
Add toolTip to SC.MenuPane items.

Added the ability to set tooltips on menu items.
Address some code review comments in memoize.
Fix issue with custom layerIds on SC.MenuPane items.

Since the menuItemViews were created before the old views were destroyed,
if those views had custom layerIds they would be removed from SC.View.views
when the old view was later destroyed.

Destroy all SC.MenuPane child views before recreating them to fix this.
Clean up SC.MenuItemView properties.

There was some inconsistency with the item*Key family of properties.

Conflicts:

	frameworks/desktop/views/menu_item.js
Fix crash on mousemove.

If a view was destroyed while the mouse was inside it, when the mouse
was then moved again a crash ocurred. The root responder tracks the
previous responder chain so it can call mouseExited on those views, but
did not check if the views had been destroyed.
Honor allowsMultipleSelection in SC.CollectionView.

A few keyboard functions were ignoring allowsMultipleSelection when
selecting multiple items.
Fix crash in interpretKeyEvents.

cmd.match could return null, but was immediately being indexed. Added a
null check.
Fix SC.ScrollerView cap sizes.

capLength and buttonOverlap did not actually match the sizes of these
elements, occasionally causing the thumb to overlap the buttons.
Fix crash in SC.SegmentedView.

Use overflowView property, which is always set, rather than relying on
childViews to find the overflow view.
Memory leak fixes.
Bumping to SC 1.9.0.12.