Add G_DBUS_SERVER_FLAGS_AUTHENTICATION_REQUIRE_SAME_USER flag
Related to !909 (merged), we should add two new flags:
G_DBUS_SERVER_FLAGS_AUTHENTICATION_REQUIRE_SAME_USER
G_DBUS_CONNECTION_FLAGS_AUTHENTICATION_REQUIRE_SAME_USER
These should eliminate the need to use the authorize-authenticated-peer
signal in common cases to check that the UID of a peer process which is requesting authorisation is the same as the UID of the D-Bus server process. This is not checked by default.