* gl/lib/randperm.c: Include randperm.h first, since it’s the API.
Include stdint.h, count-leading-zeros.h, verify.h.
(floor_lg): Rename from ceil_log (which was not actually
implementing the ceiling!) and implement the floor using
count_leading_zeros.
(randperm_bound): Use floor_lg, not ceil_log. Use uintmax_t
instead of size_t in case the size gets large on a 32-bit host.
* gl/modules/randperm (Depends-on): Add count-leading-zeros, stdint.
* gl/lib/randperm.c (randperm_new): When the number of items
to return H, is much smaller than the total number of items N,
use a hash to represent the sparse permutations of the set N.
This is currently enabled for N > 128K and N/H > 32.
* tests/misc/shuf: Ensure shuf can quickly return 2 numbers
from a large range.
* gl/modules/randperm: Depend on hash.
* NEWS: Mention the change.
