devmajor_t/devminor_t, as proposed on tech-kern.
This avoids 64-bit arithmetics and 64-bit printf formats in parts
of the kernel where it is not really useful, and helps clarity.
Instead, just add it to the list of files.
Make "prefix foo" lines actually work right when foo is an absolute path,
and make sure the length calculations correspond to the output.
Provide a way to specify a file that will always be included, and a way
to omit the prologue ("$S/") on that file.