test-c: Use g_assert_error() to make sure we get the right error message
Use G_DEFINE_QUARK for the errordomain quark

Still not sure how to stop it showing up in GtkDoc or in the VAPI though
Add .gitignore-generating magic makefile script
Add .gitignore generating stuff to Makefiles
Add VAPI metadata file to distribution tarball
Make Gtk-Doc documentation build

Not much there yet though