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Warning: don't build Ubuntu karmic liveCD with ureadahead package

------ [Warning] This is not a live-{helper,initramfs} issue, but a problem that arise because with live-helper it is so easy to build one's own live{CD,USB} ---------------------------

After using successfully live-helper to build my Ubuntu karmic liveCD, I am about to release it to my students.

As the only last minute change, I switched to using karmic-updates, and I had a big issue with *ureadahead *package which comes with karmic-updates. Boot process with 512M of RAM is very slow, only after 15 min was I able to issue a command:

free -m

the output of which is: buffers and cached show up only very few Mb, instead of the typical figures 60 and 270 I had before switching to karmic-update or with karmic-updates and ureadahead removed. The result is an unusable live system.

This ureadahead package records filesystem accesses at the first boot time for speeding up next boots by reading ahead disk in disk blocks order rather than in the order they are needed by initscripts. This clever behaviour benefits mainly to rotating hard disks drive users, if they are patient enough for not removing this package after the first boot which is much slower than before, mainly due to a bug in ureadahead which doesn't free his memory ! https://bugs.launchpad.net/ubuntu/+source/ureadahead/+bug/501715.

It is not clear if ureadahead has any benefit for SSD users. But for live{CD,USB} it is pointless, as every boot is a *first* boot, unless someone find a way to write back in the liveCD the stuff that ureadahead has recorded after booting for the first time.
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