When a ShellUserVerifier is asked to verify a user at the login
screen it will transparently first try to reauthenticate the user
against an existing session and then fall back to logging a user
into a new session. The former is used for user switching.
It's useful to know which type of verification is happening, so
the next button can be made to say "Unlock" instead of "Sign In" when
a user is already signed in.
This commit exports a new "reauthenticating" property on the
ShellUserVerifier that the auth prompt checks when deciding which
label to use for its next button.
https://bugzilla.gnome.org/show_bug.cgi?id=704795
If there are no messages in the queue and a user starts to
type then we can safely hide the message label since the
user has probably already read it.
This fixes a weirdness where "Incorrect Password" messages stay
around, even as the user types in the new correct password.
https://bugzilla.gnome.org/show_bug.cgi?id=704817
There's quite a bit of duplicated code between the login dialog
and the unlock dialog dealing with the various signals from the
ShellUserVerifier.
This commit moves that duplicated code into the AuthPrompt.
https://bugzilla.gnome.org/show_bug.cgi?id=704707
