[Unix-jun72] V2 assembler can now build the kernel

[Warren Toomey]

Now that we have the V1 and V2 binaries in the svn tree, I thought I would
try to use the V2 assembler to build the kernel, instead of the V7 one.
After a bit of experimentation, I got it to work. It means we can remove
our dependency on the V7 assembler.

I've committed tools/assemv2, the script to build with V2 as, and a patch
to redefine $mount and $gtty.

It probably means that we could rebuild the kernel while running V1; I
haven't tried this as yet.

Cheers,
	Warren