GLib freeze break for broken mimeapps.list file

[Ryan Lortie <desrt desrt ca>]

hi

We have a data corruption issue in GLib that's causing some pain:

  https://bugzilla.gnome.org/show_bug.cgi?id=658188

For some background:

  https://bugzilla.gnome.org/show_bug.cgi?id=636311

The issue is that we have a somewhat complicated algorithm that attempts
to promote the system default application for a given mimetype into the
user's list of default applications.  This code springs into play in
seemingly innocent situations (such as when calling
g_app_info_set_as_last_used_for_type() for a given type) and can do the
wrong thing.

The fix (in my opinion) is to completely remove that logic and replace
it with an extra check for system-level defaults at the time that we go
to do the query for the default app.

I'd like to push this as a last-minute change before releasing GLib
2.30.0 this afternoon.  I currently have a couple of distributions doing
testing of the change, and I'm hoping for a sign-off by Cosimo (in
addition to the one I already have from Alex).

Since this is a semi-substantial change and it comes so late in the
game, I really appreciate some extra eyeballs for review on this one, so
I'm formally requesting a freeze break (on the condition that all of the
other reviewers come back with only good news).

Cheers