Sidebar displays improperly on locationbar-less chrome pages

[michaelrhanson]

For example, the Add-ons Manager page, and about:permissions.

In these cases we should probably hide the sidebar entirely.

[mhammond]

I had a stab at this and have it mainly working in a branch bug/1-hide-on-locationbarless-chrome.

The problem with this is when the initial tab is locationbar less - eg, if about:addons is the selected tab and you then restart. It works fine in all other cases I have tried, including when you re-select that first tab.

It seems like there must be a better way though - grabbing a web progress listener seems long winded. I tried chaning for DOMAttributeChanged events etc but couldn't work out a better way. I'm over this now, so pushed the branch so I (or anyone!) can revisit.

[mhammond]

Finally found where this stuff is hidden by the browser - browser.js in an onLocationChange handler - which simplified things alot. pushed as rev 95f8558