Blender Git Loki

Bug fix #26021

Very nasty UI code issue: since every button is re-defined on a
redraw, having UI redraws while using a button was not possible.

This was solved long ago by copying over data from previous button.

However, this fails when buttons have callbacks with its own (or
a parent button) pointer.

This bug reporter found crashes in draw-overlap UI mode, this
draws entire UI over for every menu redraws, making previous button
pointers invalid. (for triple buffer, the UI is not redrawn, only
the menus).

In general: all systems falling back to old swapbuffers would have
suffered some instability because of this.

Fix is that now the old button gets lifted out from the previous
list and inserted in the new list. Works fine, but needs some tests!

Also in this commit: TIFF endian switching not needed for 16 bits tiff.