worker: make sure SavedSessionNameRead is emitted for conversations without initial username

We emit SavedSessionNameRead when we know the session associated with a
user account. Unfortunately, we don't emit the signal in the case we
don't know the username up front (such as with a smartcard).

This commit fixes it to be emitted in that case.

https://bugzilla.gnome.org/show_bug.cgi?id=740139
worker: fix typo in comment
1G#	po/zh_TW.po.rej
NEWS: update for 3.15.2
configure: bump to 3.15.2
launch-environment: Propagate XCURSOR_PATH and XDG_CONFIG_DIRS

https://bugzilla.gnome.org/show_bug.cgi?id=740632