The empty string is not too useful as an SSID, an attempt to create a
hotspot fails:
(gnome-control-center:19371): network-cc-panel-WARNING **:
Failed to add new connection: (2)
A 'wireless' setting with a valid SSID is required if no AP path was given.
Use GLib's new transliteration API to avoid the shortcomings of iconv().
Also solve an existing problem where strings entered in decomposed forms
wouldn't be properly transliterated. Always normalise before attempting
transliteration.
Bump GLib dependency to 2.39.91 for the new feature.
https://bugzilla.gnome.org/show_bug.cgi?id=724194
