If we have an input parameter (or return value) we need to use (nullable).
However, if it is an (inout) or (out) parameter, (optional) is sufficient.
It looks like (nullable) could be used for everything according to the
Annotation documentation, but (optional) is more specific.
Ignore the keyfile being deleted (ie: by the user) instead of reporting
it to the application as all values being reverted back to their
originals.
https://bugzilla.gnome.org/show_bug.cgi?id=637956
The keyfile backend forms paths like this:
prefix + group_name + '/' + keyname
If the prefix is '/apps/yelp/' and the group name is '/' then this means
that we end up with a key name of (for example):
'/apps/yelp/' + '/' + '/' + 'font-adjustment'
= '/apps/yelp///font-adjustment'
which is obviously not a valid key name.
This patch rejects group names starting or ending with '/' or containing
'//' and also rejects keys containing '/'. This should make it
impossible for invalid keys to be formed.
