Revert "Remove deprecated call to g_mapped_file_free()"
Revert "Remove deprecated call to g_mapped_file_free()"

This commit breaks older GLib. When we're ready to bump our requirement to
GLib 2.22, simply revert this commit.

This reverts commit 0ade362fb9343ec984c396a202565c4e5faa1f12 but with an
extra comment to explain what the hell is going on.

GNOME/telepathy-account-widgets,Distrotech/telepathy-account-widgets,Distrotech/telepathy-account-widgets,GNOME/telepathy-account-widgets,GNOME/telepathy-account-widgets