Patches provided by Matthias Drochner and modified by me.
Changes:
* src/spc_pdfm.c: use kpse to find media.
* dvipdfmx.c: allow inclusion of subsidiary config files, directive i
* data/config/dvipdfmx.cfg: document the i directive
* pdfdev.c (handle_multibyte_string): Handle UTP-16 surrogates
for UCS-4 supplementary planes.
The extensions provided by xdvipdfmx provide support for the Extended DVI
(.xdv) format used by xetex, including support for platform-native fonts
and the xetex graphics primitives, as well as Unicode/OpenType text.