io if it is missing.

* configure.ac:
* gegl/gegl-init.c:
* gegl/buffer/gegl-buffer-load.c:
* gegl/buffer/gegl-tile-storage.c:
* gegl/buffer/gegl-buffer-save.c:
* gegl/buffer/gegl-buffer-access.c:
* gegl/buffer/gegl-buffer.c:
* gegl/buffer/gegl-buffer-index.h:
* gegl/buffer/gegl-tile-backend-file.c:
* gegl/buffer/Makefile.am:

svn path=/trunk/; revision=2312