[xml/sgml] xerces: switching from GNU to native transcoder

[Jay Berkenbilt]

The xerces2{3,4,5} packages all build two versions: one with the ICU
transcoder and one with the GNU transcoder.  There is at least one
open bug (possibly two) that seem to be related to bugs in the GNU
transcoder.  Additionally, the Red Hat RPM .spec file included with
the xerces distribution uses the native transcoder.  Even building the
released xerces packages require a patch to use the GNU transcoder
with gcc, which suggests that the xerces developers don't use it much
on Linux.  I ran this past the xerces-c-dev mailing list and didn't
get any replies.

I have several small changes to the xerces packages to close most of
the bugs posted against them and to use libicu28 instead of the very
old libicu21 packages.  I'm also planning on switching from the GNU to
the native transcoder for the default version of the library.  An ICU
transcoder version will also be available.  I'm not planning on adding
a third version for the GNU transcoder.

If anyone can think of a reason not to do this, let me know.  Thanks!
(I won't wait for replies before preparing the updated packages.)

--Jay