Get rid of the artification limitation enforced by
SCTP_AUTH_RANDOM_SIZE_MAX.
This was suggested by Andrew Galante.

MFC after: 3 days
Add a 'mini-memstick.img' release target, which will use the
'bootonly.iso' components to create a smaller memory stick image.

This is useful for system recovery, where a full memstick.img image
is not necessarily needed (or wanted).  In addition, it is possible to
do bootonly-style installation, where the base.txz, kernel.txz, etc.
are fetched from a remote source.

Provide backwards-compatible target (mini-memstick), to keep in sync
with the targets documented in release/Makefile.

Prompted by:	wblock
MFC after:	1 week
X-MFC-after:	10.0-RELEASE
Sponsored by:	The FreeBSD Foundation
Remove extra target from 'memstick' that I forgot to remove before
previous commit.

MFC after:	1 week
X-MFC-After:	10.0-RELEASE
X-MFC-With:	r257805
Sponsored by:	The FreeBSD Foundation
Update release(7) to include 'mini-memstick' after r257805.

MFC after:	1 week
X-MFC-After:	10.0-RELEASE
X-MFC-With:	r257805, r257806
Sponsored by:	The FreeBSD Foundation