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

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

The sigconv.awk script generates a sigdesc.h header file, which
contains a sigdec[] vector of structures, but the generated output is
missing braces around the initializer of each struct, which
triggers warnings in WARNS=3:

src/usr.bin/top/sigdesc.h:10: warning: missing braces around initializer
src/usr.bin/top/sigdesc.h:10: warning: (near initialization for `sigdesc[0]')

* Fix the sigconv.awk script to generate a header with initializers
which look better.

* Add rules to usr.bin/top/Makefile that rebuilds a new sigconv.h
header which matches the correct signal set from the build-time
version of `${DESTDIR}/usr/include/signal.h' (so sigconv.h doesn't
get stale once changes are made to the header).

* Remove the old sigconv.h header, now that it is autoupdated at
build time.

* Various Makefile style fixes (the committed Makefile was kindly
submitted by Ruslan):

- Reorder .PATH, PROG, SRCS and CFLAGS to match style.Makefile(5)
- Split off the generated sources (sigdesc.h top.local.h) in an
SRCS+= line of their own.
- Add entries to CLEANFILES near the rules that generate the
respective files.
- Move the explicit rule which builds top.1 after the implicit
rules which generate its dependencies.

Reviewed by: ru, bde
Submitted by: ru (Makefile)
MFC after: 2 weeks

This commit was generated by cvs2svn to compensate for changes in r24139,
which included commits to RCS files with non-trunk default branches.

This is the long-awaited import of top into the base system (actually,
the src/contrib/top part right now). This tools is simply too system-
dependant to maintain it in the ports collection.