Chili FTL's RTT isn't updated properly

[gajop]

There are a number of issues in different projects with the UI not being redrawn properly. Sometimes it's caused by updating a control in a ScrollPanel that's not visible, but there are other cases as well.

These are all errors or hacky workarounds related to this issue:

• https://github.com/jk3064/chiliui/issues/33
• https://github.com/Spring-Chobby/Chobby/issues/46
• Hacky workaround that still uses RTT: https://github.com/gajop/Scened-Core/blob/master/scen_edit/view/editor_view.lua#L54-L111
• Disabling RTT (https://github.com/Spring-Chobby/Chobby/commit/9b5143d0eb9e00cce21eb5cf36eaa1c6274fd61a) seems to make things render properly.

I knew about this bug for a long time now (1+year), but it's not trivial to reproduce with a single widget, and all my fast attempts to debug it have failed. We now know that it's in RTT (and probably not LayoutPanel or ScrollPanel), so it might narrow the search area, but I haven't done that yet.

This is a critical bug that makes FTL Chili unusable. I think if it were fixed we could see FTL Chili in projects like ZK much sooner.