background: Fix test-chooser-dialog build with some linkers

List missing libs for the libbackground-chooser.la convenience library.

https://bugzilla.gnome.org/show_bug.cgi?id=709302
background: Fix compilation with libsocialweb support

The flickr source files were added to the wrong internal shared
library, so that the panel could be linked, but not the test
application.

https://bugzilla.gnome.org/show_bug.cgi?id=710829