Copy stable/9 to releng/9.3 as part of the 9.3-RELEASE cycle.

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

Copy head to stable/9 as part of 9.0-RELEASE release cycle.

Approved by: re (implicit)

Revise r197763 which fixes filesystem corruption when extending
into un-zeroed storage.

The original patch was questioned by Kirk as it forces the filesystem
to do excessive work initialising inodes on first use, and was never
MFC'd. This change mimics the newfs(8) approach of zeroing two
blocks of inodes for each new cylinder group.

Reviewed by: mckusick
MFC after: 3 weeks