Add --distribution option to choose which distribution of Debian to use.

Add --distribution option to choose which distribution of Debian to use.
Add --user option to specify username to create, default olpc.
Add --mirror option to allow a local package mirror to be used, tested
to work with the approx package.
Add --othermirror optioin to allow an addition sources.list line.
Add --package-list option.
Move chroot mount and umount to functions for shell use.
Add package lists for lxde and kde.
Cache the kernel package.
Only configure xorg.conf, Gnome, or KDE files if they are present.
Add user to the floppy group for thumb drive use.