file-chooser: Don't wait for ENTER to initiate search

Most of the core GNOME applications (eg., gnome-control-center,
gnome-documents, and nautilus) start searching as soon as the text
changes, and don't wait for the user to hit ENTER. It would be nice to
follow the same pattern.

https://bugzilla.gnome.org/show_bug.cgi?id=739977
places sidebar: Fix the sort function

When returning 1 for a pair (a,b), a sort function must
return -1 for the pair (b,a), otherwise things can go
badly.

https://bugzilla.gnome.org/show_bug.cgi?id=739729