GZDoom used to have hardcoded MessageBox menu selector, 0x0d character
of console font, while the other menu is displayed is SmallFont.
It looked too ugly if SmallFont and ConFont heights are different,
and also there was no method of modifying the selector.
Now, the selector is 0x0d from SmallFont, if SmallFont contains this glyph
(its height is greater than zero), otherwise it falls back to previous
behavior (using ConFont as a source of this glyph).
To define custom MessageBox menu selector, just define 0x0d glyph for
SmallFont, and it will be displayed in the menu.
The gap between selector and menu options text is 3 pixels (as before), and
if you wish to enlarge this gap, just add some transparent columns at the
right side of 0x0d glyph.
* Emit a warning when relational comparisons are made between signed and unsigned ints.
* Handle shift operators so that they do not fail for constant definitions.
* changed return type of Array::Size() to signed int as most code out there is using it this way and would otherwise drown in warnings.
* fixed a few deprecation warnings.
Enables shortcuts for option menus. Press a key to immediately jump to the next
option menu entry which starts with this key. Hold Alt to jump backwards.
Compatible with localized menus (checked on Russian).
