As it turns out, we have examples of internal functions called
type_name_get_private() in the wild (especially among older libraries),
so we need to use a name for the per-instance private data getter
function that hopefully won't conflict with anything.
Found by GIR compiler when building gobject-introspection:
gir/gio-2.0.c:33525: Warning: Gio: g_tls_password_set_description: unknown
parameter 'flags' in documentation comment, should be one of 'password',
'description'
gir/gio-2.0.c:14568: Warning: Gio: g_action_group_action_state_changed: unknown
parameter 'state' in documentation comment, should be one of 'action_group',
'action_name', 'value'
The database is an abstract object implemented by the various TLS
backends, which is used by GTlsConnection to lookup certificates
and keys, as well as verify certificate chains.
Also add GTlsInteraction, which can be used to prompt the user
for a password or PIN (used with the database).
https://bugzilla.gnome.org/show_bug.cgi?id=636572
