Change: extending the support up to Firefox 4.0 thru couple minor changes
New: attribute 'multiselection' added to menu items

The presense of the attribute denotes the xul element support tab
multiselection and can be set true/false if there are some tabs
multiselected. This will be used to highlight the xul elements (i.e. menu
items).
This attribute wont be forward compatible once multiselection lands in
Firefox (as 'multiselected' attribute probably will be).
Change: update 'multiselection' attribute on showing tab context menu
Change: new css definition of multiselected tab and menuitems.

Using OS selection colors and red triangle.
New: tab border image for multiselected tabs.
Change: css overlay updated to use border image
New: multiselection broadcasters added

The observers simplify determining when there are tabs multiselected and
the xul changes that follows.
Change: onpopupshowing handler now updates multiselectionContextBroadcaster
New: the 'multiselected' attr. setter updates multiselectionBroadcaster
Change: menuitems now listen to the multiselection broadcasters
Merge branch 'feature/v12-selection' into feature/css-selection
Merge branch 'feature/observers'
Merge branch 'feature/css-selection'

Conflicts:
	README.md
	chrome/content/browserOverlay.css