Moving expat and a few other libraries to the base system

[Bernd Ernesti <veego%NetBSD.org@localhost>]

Hi,

as seen over the last months there is a problem for some people
who want to install binary package which depends on the Xorg
expat library but they don't have the X11 sets installed.

The idea which came up was to move the expat library out of
the X11 sets into the base set.
At the same time the source code will have to move too.
From xsrc/external/mit to src/external/mit/expat/dist (not sure
if that looks so good with the existing xorg directories below
src/external/mit).

Joerg also mentioned that two more libraries could move too:
 freetype
 fontconfig

What do other think about such changes?

Bernd