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

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

Make paths an explicite datatype instead of using the generic Lst.
A Path is now a TAILQ of PathElements each of which just points to
a reference counted directory. Rename all functions dealing with Paths
from the Dir_ prefix to a Path_ prefix.

Reorganize Suff_EndTransform to be called only for nodes for
which it is needed (transforms).

Clean up include files and file including. Split nonints.h into pieces
that get included just where they are needed. All headers include the
headers that they need to compile (just with an empty .c file). Sort
includes alphabetically where apropriate and fix some duplicate commenting
for struct Job, struct GNode and struct Shell by removing one version and
inlining the comments into the structure declaration (the comments have been
somewhat outdated).

This patch does not contain functional changes (checked with md5).

Submitted by: Max Okumoto <okumoto@ucsd.edu>