winedos/int10 clearscreen fix

[Ulrik Mikaelsson]

Hi

I've had issues with a console program not clearing the screen when it's 
supposed to. I've traced the problem down to dlls/winedos/int10.c function 
DOSVM_Int10Handler() with and AH reg of 0x0b.

I've added code for clearing the screen with the specified color, as well as 
added a method for doing a total clearscreen to vga.c and vga.h.

It's only tested for textmode and propably won't work for anything else so I 
think the fixme should be left for anyone who's up for the task.

A patch is attached, please feel free to comment before i submit to 
wine-patches.

Regards
Ulrik