String change in gnome-session

[Matthias Clasen <matthias clasen gmail com>]

I'd like to commit the string change in
https://bugzilla.gnome.org/show_bug.cgi?id=644461

This is about the startup message we show when we have to go to
fallback mode because of lack of hw accel. The current string is not
grammatically correct and reads a bit awkward.

It is a fairly new string and may not yet be widely translated anyway.

Ok, to commit ?