*** Updating the kernel configs ***

- Copy the old Nix expression (e.g. linux-2.6.21.nix) to the new one
  (e.g. linux-2.6.22.nix) and update it.
- Add an new attribute to all-packages.nix.
- Unpack the new kernel.

For each platform (i686, x86-64, uml):

- Make an svn copy from the old config (e.g. config-2.6.21-i686-smp)
  to the new one (e.g. (e.g. config-2.6.22-i686-smp).
- Copy the config file for this platform
  (e.g. config-2.6.22-i686-smp) to .config in the kernel source tree.
- Run `make oldconfig ARCH={i386,x86_64,um}', answer all questions.
  (For the uml configuration, also add "SHELL=bash".)
- Make sure that CONFIG_FB_TILEBLITTING is NOT SET (otherwise fbsplash
  won't work).  If it is, investigate why (there's probably another
  option that forces it to be on) and fix it.
- Copy .config over the new config file (e.g. config-2.6.21-i686-smp).