- No more limit on the number of preseed parameters, by placing a preseed.cfg
  file inside the initrd, instead of passing them all via the command line.
  The kernel is usually limited to 32 parameters and it panics when there are
  too many.

- Dist-specific options.

- Recognize preseed aliases.

- late-command is run with '/bin/sh -e' and it must exit with EX_OK (0),
  otherwise the installer stops.