mail demo failing on trunk (IE)

[bill]

Mail demo fails to load on IE w/an exception. Works on 1.2 but failing on trunk.

Looks like the error in BorderContainer? initializing when hidden, although my latest checkins should have fixed that.

Also need to find the other ticket about BorderContainer failing initialization due to negative values, and reopen it (in favor of this ticket)

[bill]

(In [15959]) Rollback some of the changes from [15876], which broke mail demo:

TabContainer/StackContainer? should not do sizing in startup(), since, as stated in _LayoutWidget.startup().

In this case the mail demo was failing because:

• the outer BorderContainer? (main) contains a TabContainer? whose first child is another BorderContainer? (inbox)
• the outer BorderContainer? correctly calls startup() on it's child TabContainer? before setting the size of the child.
• thus the TabContainer? and it's child BorderContainer? (inbox) thought that height==0
• inner BorderContainer? (inbox) failed on initialization b/c it tried to set things to negative height

Fixes #8205, refs #5220 !strict