SDL queues up all the input events received in a frame. When the hotkey
system saw a key up/down event, it immediately updated its
HotkeyIsPressed state and then pushed a hotkey event onto the end of the
queue.
If the initial queue was e.g. [key-down shift, key-press Z, key-up
shift], the hotkey event triggered by Z would be processed after the
key-up shift had updated the HotkeyIsPressed state, so the handler of
the Z hotkey would not think the shift hotkey was pressed.
If the initial queue was e.g. [key-press Z, mouse-click], the hotkey
triggered by Z would be processed after the mouse-click event, so it
could apply to the wrong building selection.
Fix by pushing the hotkey events onto a special queue that gets
processed before any subsequent SDL input events.
Also update the HotkeyIsPressed status when the HOTKEYDOWN/HOTKEYUP
events are processed, not when they are generated, to guarantee they are
consistent with the DOWN/UP events.
Fixes#1869.
This was SVN commit r14057.
2d1be3d47e