Set a default trust store for GnuTLS
Otherwise, the changes I am planning in https://bugzilla.gnome.org/show_bug.cgi?id=753260 are going to break glib-networking for Flatpak.
See https://github.com/flatpak/freedesktop-sdk-base/commit/0f966a64bab45c580d22e4ea0d96ccb7e2f60b93
Fixes #80 (closed)
Edited by Adam Jones