(ctagsfiles): Split so that files starting

(ctagsfiles): Split so that files starting
with an `x' are found before files starting with `w32'.
(ctagsfiles1): New.
(ctagsfiles2): New.
(TAGS): Use ctagsfiles[12] instead of ctagsfiles.
Add PNG library.
(obj): Add sound.o.
(LIBW): Use Xaw3d if present.
(LIBTIFF): Added.
(LIBJPEG): Added.
(LIBXPM): If not already defined, define to -lXpm.
(LIBX)[HAVE_X11]: Add LIBXPM.
(term.o): Add dependency on dispextern.h.
(alloc.o): Add dependency to dispextern.h.
(window.o): Depends on dispextern.h.
(alloc.o): Add dependency dispextern.h.
(window.o): Add dependency window.c -> dispextern.h
(term.o): term.c depends on dispextern.h