Added drand48(3), lrand48(3), mrand48(3).

These had been lying around for a while, partially because they aren't
very interesting, but mostly because the implementations from eglibc,
dietlibc and musl libc (with the same seeds) give different results.

This is ridiculous, but it also happens to have a very low priority on
my todo list.

The mtime is recent because I modified some comments.
Added George Marsaglia's SUPRKISS.

SUPRKISS32 is implemented and seems to work (testing would take days);
SUPRKISS64 should be trivial to get right, but I'd need a computer where
vim's integers are 64 bits wide to make sure it works;
there's currently no srand().

I waited to commit because I wanted to run at least one iteration of the
test procedure -- it took my (old) computer 468 seconds: the remaining
999 iterations are left as an exercise for the reader.

Seriously, the occasional refill() is so slow it takes a few seconds,
but I've added it anyway because I find it ironic (in a sick way).

BTW, the algorithm passes dieharder even without seeding.