Copy head (r256279) to stable/10 as part of the 10.0-RELEASE cycle.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Revert previous commit...

Pointyhat to: kevlo (myself)

Prefer NULL over 0 for pointers

Avoid 256 integer divisions per rc4_init() call. Replace it with using
separate index variable.

It gives more then double rc4_init() performance increase on tested i386 P4.
It also gives about 15% speedup to PPTP VPN with stateless MPPE encryption
(by ng_mppc) which calls rc4_init() for every packet.

Use __FBSDID().

make rc4 crypto support a module so other modules can depend on it

Submitted by: imp
Reviewed by: imp

Forced commit. This is to try and help folks that used the international
crypto repo and have slightly different files but with the same version.
cvsup in 'checkout mode' has no trouble with this, but cvs can get really
silly about it.

Clarification to previous commit: this code implements the algorithm
which is commonly referred to under the trademarked name 'RC4'.
However, this is not the actual 'RC4' implementation.
(Forced commit)

A simplified RC4 implementation for kernel use.