* examples/example_project_manager.glom: This is just so we
use this layout item somewhere, so we can test it.
        * glom/glom_document.dtd: Mention the layout_item_image tag.
* configure.ac:
* Makefile_tests.am:
* tests/test_document_load_image.cc: Add a new test for this
feature, using GdkPixbufLoader to check that we can interpret
the data as an image.