Make di_blocks unsigned in UFS1 as is the case already for UFS2.

Most of the code between UFS1 and UFS2 is shared so this change
is pretty safe. Not only this makes UFS1 and 2 consistent but it
also matches what NetBSD and MacOS X have for some years now.

Reviewed by:	mckusick
MFC after:	1 month
Rename libbsdyml to libyaml, make private, and bump
SHLIB_MAJOR to 1.0

Suggested by:	des
Approved by:	bapt
MFC after:	1 week