Fix up copyright information
Trivial include cleanup
Add some tests for pixbuf-form-stream apis
Add some tests for resource APIs
Try to fix the continuous build

We are using to-pixdata processing for some of the resources
in tests/, but gdk-pixbuf-pixdata has not been installed on
the system yet. So pass the location of the just-built one
via the GDK_PIXBUF_PIXDATA env var.
Try harder to fix the continuous build

To use gdk-pixbuf-pixdata uninstalled, we need to use the
uninstalled modules as well, so set GDK_PIXBUF_MODULE_FILE
as well.