Sub-directories inside gio/ already processed in a previous commit:
- fam/
- gdbus-2.0/ (which contains only codegen/)
- gvdb/
- inotify/
- tests/
- win32/
- xdgmime/

Other sub-directories inside gio/:
- completion/: no license headers
- kqueue/: not LGPL, BSD-style license

https://bugzilla.gnome.org/show_bug.cgi?id=776504

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.

See https://developer.gnome.org/hig/stable/typography.html

https://bugzilla.gnome.org/show_bug.cgi?id=772221

This makes them easier to identify when debugging and profiling.

This patch was somewhat less than interesting to write.

https://bugzilla.gnome.org/show_bug.cgi?id=767765

When emitting the RESOLVING/RESOLVED events the connection param is
set to NULL.

g_socket_client_add_application_proxy() claimed "When the indicated
proxy protocol is returned by the #GProxyResolver, #GSocketClient will
consider this protocol as supported but will not try to find a #GProxy
instance to handle handshaking." But in fact, it did the checks in the
wrong order, so GProxy proxies ended up overriding
application-specified ones. Fix that.

Also, simplify the code a bit by making use of g_hash_table_add() and
g_hash_table_contains().

https://bugzilla.gnome.org/show_bug.cgi?id=733876

If a g_socket_client_connect_async() operation is cancelled between the
CONNECTING and CONNECTED events (i.e. while in the
g_socket_connection_connect_async() call), the code in
g_socket_client_connected_callback() would previously unconditionally
loop round and try the next socket address from the address enumerator
(by calling enumerator_next_async()). This would correctly handle the
cancellation and return from the overall task — but not before emitting
a spurious RESOLVING event.

Avoid emitting the spurious RESOLVING event by explicitly handling
cancellation at the beginning of g_socket_client_connected_callback().

https://bugzilla.gnome.org/show_bug.cgi?id=735179

https://bugzilla.gnome.org/show_bug.cgi?id=726611