- Copy stable/10 (r259064) to releng/10.0 as part of the
10.0-RELEASE cycle.
- Update __FreeBSD_version [1]
- Set branch name to -RC1

[1] 10.0-CURRENT __FreeBSD_version value ended at '55', so
start releng/10.0 at '100' so the branch is started with
a value ending in zero.

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

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

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

Fix usage for soreceive(9) - uio must always be non-NULL.

MFC after: 1 week

Reference socket(9) from ng_ksocket(4). Reference ng_ksocket(4),
ithread(9), msleep(9), ucred(9) from socket(9).

Partly suggested by: julian

Add a basic man page for the socket(9) kernel programming interface used
by the NFS client and server, netsmb, netncp, etc.

Reviewed by: ru
Fixed by: ru