SDL_HOTKEYUP being sent while typing text

[elexis]

Before and after r19028, SDL_HOTKEYUP events are sent when typing in input boxes. For example WASD will trigger the key-release events of the camera movement hotkeys.

No HOTKEY events (neither UP nor DOWN) may be sent in text input mode (so that the player can type text without causing unintended actions). This can also be seen in Gamesetup.cpp:

// gui_handler needs to be registered after (i.e. called before!) the
// hotkey handler so that input boxes can be typed in without
// setting off hotkeys.

Because these events are currently unused (except the 2 GUI refresh calls when releasing the shift key introduced in that commit), vanilla 0 A.D. doesn't appear to bugged to the player - yet.