Add 'default' parameter to setButtons, that controls the binding
of Return (unless overridden) and applies the 'default' pseudo-class.
Currently it has no effect, but it will start having after the
login dialog redesign.
https://bugzilla.gnome.org/show_bug.cgi?id=619955
* Add a keyring prompter based on GcrSystemPrompter
* Adds dependency on gcr version 3.3.5 or higher
* Not yet using unmerged support for non-pageable memory
https://bugzilla.gnome.org/show_bug.cgi?id=652459