Avoid embedding buffers into static virtual terminal window.

MFC after:	1 week
Sponsored by:	The FreeBSD Foundation
Initialize zfs vnode v_hash when the vnode is allocated, instead of
postponing it to zfs_vget().  zfs_root() returned vnode with the
default value of v_hash, which caused inconsistent v_hash value when
root vnode was obtained from zfs_vget().

Nullfs allocated two upper vnodes for the root zfs vnode due to
different hashes, causing consistency problems.

Reported and tested by:	Harald Schmalzbauer <h.schmalzbauer@omnilan.de>
Sponsored by:	The FreeBSD Foundation
MFC after:	1 week
For md(4), posix shm(3) and tmpfs(5), free swap space used by paged in
dirty page, which is written by the process.

Reviewed by:	alc
Tested by:	pho
Sponsored by:	The FreeBSD Foundation
MFC after:	1 week
Fix r269183 build woth GCC.

MFC after:	2 weeks
Remove special handling of console window size. It's done in vt_upgrade() for
all windows.

MFC after:	1 week
Sponsored by:	The FreeBSD Foundation
Update comments.

MFC after:	1 week
Sponsored by:	The FreeBSD Foundation
Revise font initialization handling.

MFC after:	1 week
Sponsored by:	The FreeBSD Foundation