[freespace2] G400 text problem... someone test this

[Bradley Bell]

Quoting Taylor Richards <mtrs at bellsouth.net>:

> Clearing the zbuffer after the shader fixes this for me but I'm only
> looking at the mainhall.  If someone wouldn't mind, test this to see if
> it gets all of the issues on the HUD too.  I don't think there are any
> adverse effects from this (speed wise or other).  If there is a better
> or more complete way of doing this please let me know.  If this patch
> doesn't work for you on the mainhall then you're doing it wrong ;-)

Yep, it fixes it for the mainhall, and fixes it for the hud most of the time. 
It still does it occasionally, such as whenever I collide with anything, so it
could be related to the flashing "collision" text.

-brad