MFC: r300956

MFC: r300956

1) Unifdef USE_WEAK_SEEDING since it is too obsolete to support and makes
reading hard.

2) Instead of doing range transformation in each and every function here,
do it single time directly in do_rand(). One "mod" operation overhead is not
a big deal, but the code looks nicer and possible future functions additions
or PRNG change do not miss range transformations neither have unneeded ones.

3) Use POSIX argument types for visible functions (cosmetic).

git-svn-id: svn://svn.freebsd.org/base/stable/10@301445 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f