streams code - setup HEAD

[Robert Collins]

I've checked in my partial streams code. It's fully self contained, but
not extended to cover network io yet.

If you have a sandbox on HEAD, make a diff before updating, this will
make sorting conflicts (if any) easier.

A few key notes:
* the cflags have been changed to include

CFLAGS          :=
@CFLAGS@ -Werror -Winline -Wall -Wpointer-arith -Wcast-align\
        -Wwrite-strings -Wstrict-prototypes -Wmissing-prototypes \
        -Wmissing-declarations -Wcomments

automatically. This is possibly not the best place to make the change,
but hey :}.

* I haven't tried -O3 with setup, and as that makes the binary bigger,
I'm not sure if it's a good idea. Setup.exe shouldn't have any
performance problems anyway.

This version supports plain old .tar files in addition to .tar.gz and
.tar.bz2. This was (quite literally) a freebie once the tar and compress
functions where split up.

I'd like to thank Warren Young for the time and effort he put into
designing the class hierarchy, which I've extended slightly, as having a
clear hierarchy in advance made a lot of the code trivial.

Rob