Remove support for XFree8-4.

From now on, X_WINDOW_SYSTEM != "xorg" is not supported anymore.

PR:             ports/119418
Submitted by:   flz
Approved by:    portmgr (pav)

- Welcome X.org 7.2 \o/.
- Set X11BASE to ${LOCALBASE} for recent ${OSVERSION}.
- Bump PORTREVISION for ports intalling files in ${X11BASE}.

Replace ugly "@unexec rmdir %D... 2>/dev/null || true" with @dirrmtry

Approved by:    krion@
PR:             ports/88711 (related)

If port belongs to X11 distribution different than ${X_WINDOW_SYSTEM} one,
point to The X Window System and Virtual Consoles chapter of FAQ.

Add SHA256.

Upgrade to XFree86 4.5.0.

Ports changes:
- Drop dependency on x11/wrapper. X server already contains this code
(programs/Xserver/os/utils.c rev. 3.58).
- Install default SecurityPolicy with XFree86-4-libraries, thus avoiding
plists and who-owns-what complications between different fooServer ports.
Copy default file to real one if that doesn't exist and remove both upon
uninstall if they are the same.
- Revert change to Imake.rules rev. 3.132 in devel/imake-4 port, since
couple of ports break with this change
(devel/imake-4/files/patch-Imake.rules)
- Add grehans patches for PPC [1]
- Several of directories that were previously in /etc/mtree/BSD.x11-4.dist
were moved to respective ports pkg-plists

PR:             [1] 78345, 78346, 78348, 78352, 78353, 78354, 78355, 78356

Update X.Org ports to 6.8.1, and the DRI port to use Mesa 6.2.  Because Mesa 6.2
DRI drivers are incompatible with the old libGL in XFree86, they have been
repocopied to graphics/xfree86-dri.  Also note that with this commit the html
manpages are going away, and with it the runtime dependency on perl for the
imake port.

Release notes at: http://www.x.org/X11R6.8.1/RELNOTES.txt

Props to:       kris (multiple cluster runs and sorting through logs)
                lesi (fixing all the issues in those logs, and more)