reiserfs now have separate modules that are conditional on
boot.supportedFilesystems and boot.initrd.supportedFilesystems.
By default, these include the filesystems specified in the fsType
attribute in fileSystems. Ext2/3/4 support is currently
unconditional.
Also unbreak the installer test (http://hydra.nixos.org/build/2272302).
svn path=/nixos/trunk/; revision=32954
