MFC r227519, r227520:

MFC r227519, r227520:

r227519 (das)

Sync the style, comments, and variable names of arc4random.c with
OpenBSD's version (r1.22).  No functional changes, as verified with
md5.

r227520 (das)

Further reduce diffs with OpenBSD's arc4random.  The main functional
change here is to ensure that when a process forks after arc4random
is seeded, the parent and child don't observe the same random sequence.
OpenBSD's fix introduces some additional overhead in the form of a
getpid() call.

The only significant remaining difference between our arc4random and
OpenBSD's is in how we seed the generator in arc4_stir().

git-svn-id: svn://svn.freebsd.org/base/stable/8@267380 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f