international keyboard support (revisited)

[Tony J. White]

https://bugzilla.icculus.org/show_bug.cgi?id=2741

Discussion of this hasn't brought up any compelling reason not to add the
Shift-Esc toggleConsole bind (that I noticed).

It seems that most of the confusion about using the '~' character on
many international keyboards stems from SDL's recent change in "Dead Key"
handling.  For example, I think keying Shift-Esc on a .de keyboard will
be preferred over typing "AltGr-'+' SpaceBar" for those who know about it.
Also, it gives an easy way to explain how to open the console in-game.
Shift-Esc is much easier to communicate than trying to tell someone to
type a key that you can't type in the game and then explaining to them
that they may or may not need to type a space after it.

My latest patch also adds a new section to the README called
"SDL Keyboard Differences" which explains this and other SDL-specific
differences.

On another note, I've added Christophe's additional key support code
to my latest patch.  This supports all the SDLK_WORLD keys as well as
a several other keys not otherwise supported like "SCROLLLOCK", "SYSREQ",
"WINDOWS", "F13", "F14", "F15", and a few others.  This may be
controversial since it will allow people to set up binds with the
SDL client that will not be compatible with the win32 ioquake3 client or
id Quake3.  Thoughts?

-Tony