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

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

Mechanically substitute flags from historic mbuf allocator with
malloc(9) flags within sys.

Exceptions:

- sys/contrib not touched
- sys/mbuf.h edited manually

Mark MALLOC_DEFINEs static that have no corresponding MALLOC_DECLAREs.

This means that their use is restricted to a single C file.

Use m_unshare()+m_copyback() instead of m_freem()+m_devget() to keep
original mbuf chain headers. It can be less efficient in some cases, but it
looks better then mess of copying headers into the nonempty chain.

Slightly simplify code.

Whitespace cleanup.

Checked with: cvs diff -b

A node that implements Predictor-1 compression for PPP.

Submitted by: Alexander Motin <mav alkar.net>