Log Message:
Make xdm use configs from under PKG_SYSCONFDIR.
Some ideas came from NetBSD's XFree86 customizations.

Use USE_PKGINSTALL and CONF_FILES for xorg-clients.
Installs xdm configs (and shell scripts) to examples directory.
Create OWN_DIRS for the authDir.

PLIST changes are for chooser is now in bin directory.
And pixmaps moved to include/X11/pixmaps directory.
xdm configs are no longer in lib/X11/xdm (so they are no longer lost
on reinstall).

(Anyone want to do twm and other configs?)