Extend pango to emulate the circle character and then use it
in gdm etc. (perhaps as the general gtk default passwd char,
if we can)
Probably post-this-release but as it came up late this cycle,
putting it in for tracking next time.
The only way to do this is to ship a font with Pango with the character.
Upstream is http://bugzilla.gnome.org/show_bug.cgi?id=63633