- Copy stable/10@296371 to releng/10.3 in preparation for 10.3-RC1
builds.
- Update newvers.sh to reflect RC1.
- Update __FreeBSD_version to reflect 10.3.
- Update default pkg(8) configuration to use the quarterly branch.

Approved by: re (implicit)

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

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

On those machines, where sf_bufs do not represent any real object, make
sf_buf_alloc()/sf_buf_free() inlines, to save two calls to an absolutely
empty functions.

Reviewed by: alc, kib, scottl
Sponsored by: Nginx, Inc.
Sponsored by: Netflix

Implement basic support for memory attributes. At this time we only
distinguish between UC and WB memory so that we can map the page to
either a region 6 address (for UC) or a region 7 address (for WB).

This change is only now possible, because previously we would map
regions 6 and 7 with 256MB translations and on top of that had the
kernel mapped in region 7 using a wired translation. The introduction
of the PBVM moved the kernel into its own region and freed up region
7 and allowed us to revert to standard page-sized translations.

This commit inroduces pmap_page_to_va() that respects the attribute.

MFamd64
Simplify the sf_buf implementation. In short, make it a veneer
over the direct virtual-to-physical mapping.

- Modify alpha's sf_buf implementation to use the direct virtual-to-
physical mapping.
- Move the sf_buf API to its own header file; make struct sf_buf's
definition machine dependent. In this commit, we remove an
unnecessary field from struct sf_buf on the alpha, amd64, and ia64.
Ultimately, we may eliminate struct sf_buf on those architecures
except as an opaque pointer that references a vm page.