lowmem

It seems silly to call between 32 and 48 mb of memory "lowmem", but so it is in current d-i. Today I got the minium memory requirements back down to 32 mb, from 44 mb. I added a lowmem udeb which provides a whole low memory infrastructure, with various hooks. This should help someone who really cares about low memory support to get things down to 24 mb or so, I think. I still belive that 16 mb installs should be possible, but it would require some significant work on d-i.