Log message:
Simply and speed up buildlink3.mk files and processing.
This changes the buildlink3.mk files to use an include guard for the
recursive include. The use of BUILDLINK_DEPTH, BUILDLINK_DEPENDS,
BUILDLINK_PACKAGES and BUILDLINK_ORDER is handled by a single new
variable BUILDLINK_TREE. Each buildlink3.mk file adds a pair of
enter/exit marker, which can be used to reconstruct the tree and
to determine first level includes. Avoiding := for large variables
(BUILDLINK_ORDER) speeds up parse time as += has linear complexity.
The include guard reduces system time by avoiding reading files over and
over again. For complex packages this reduces both %user and %sys time to
half of the former time.

Log message:
Include pyversion.mk include the protected part of the buildlink3.mk
files, not over and over again.

Log message:
Add DESTDIR support.

Log message:
Fixed name mismatch.

Log message:
Fixed the separation of CONFIGURE_SCRIPT and CONFIG_SHELL.

Log message:
Change the format of BUILDLINK_ORDER to contain depth information as well,
and add a new helper target and script, "show-buildlink3", that outputs
a listing of the buildlink3.mk files included as well as the depth at
which they are included.

For example, "make show-buildlink3" in fonts/Xft2 displays:

	zlib
	fontconfig
	    iconv
	    zlib
	    freetype2
	    expat
	freetype2
	Xrender
	    renderproto

Log message:
Track information in a new variable BUILDLINK_ORDER that informs us
of the order in which buildlink3.mk files are (recursively) included
by a package Makefile.

Log message:
pyversion.mk only needs to be included once.

Log message:
Aligned the last line of the buildlink3.mk files with the first line, so
that they look nicer.

Log message:
Over 1200 files touched but no revisions bumped :)

RECOMMENDED is removed. It becomes ABI_DEPENDS.

BUILDLINK_RECOMMENDED.foo becomes BUILDLINK_ABI_DEPENDS.foo.

BUILDLINK_DEPENDS.foo becomes BUILDLINK_API_DEPENDS.foo.

BUILDLINK_DEPENDS does not change.

IGNORE_RECOMMENDED (which defaulted to "no") becomes USE_ABI_DEPENDS
which defaults to "yes".

Added to obsolete.mk checking for IGNORE_RECOMMENDED.

I did not manually go through and fix any aesthetic tab/spacing issues.

I have tested the above patch on DragonFly building and packaging
subversion and pkglint and their many dependencies.

I have also tested USE_ABI_DEPENDS=no on my NetBSD workstation (where I
have used IGNORE_RECOMMENDED for a long time). I have been an active user
of IGNORE_RECOMMENDED since it was available.

As suggested, I removed the documentation sentences suggesting bumping for
"security" issues.

As discussed on tech-pkg.

I will commit to revbump, pkglint, pkg_install, createbuildlink separately.

Note that if you use wip, it will fail!  I will commit to pkgsrc-wip
later (within day).