wpp: add I/O hooks [try 2]

[Matteo Bruni]

Hi Juan,

these I/O hooks are needed to use wpp as a preprocessor for d3d shader
assembling, where I have to read files with CreateFile/ReadFile
(Windows-style) or from memory. I plan to send the assembler patches
not immediately (in particular, the patch which makes use of wpp is
not so near). On the other hand, having the possibility to see how I
use these callbacks can be indeed useful to do a review.
So I think I'm going to wait until tomorrow: if this patch doesn't go
in, I will postpone it to the moment I strictly need this.

2009/7/15 Juan Lang <juan.lang at gmail.com>:
> Hi Matteo,
>
> it'd be easier to review your patch if you sent it along with a
> subsequent patch that made use of the I/O hooks.  As it is, it's hard
> to know why this is necessary.
>
> Cheers,
> --Juan
>