Python 2 reached EOL on 2020-01-01, and the latest version of
AX_PYTHON_DEVEL breaks the build with Python 2. This seems as good a
time as any to drop compatibility.

Signed-off-by: Simon McVittie <smcv@collabora.com>

Back in the days of PyGTK, there was only the gobject module, containing
bindings for both GLib and GObject. This is no longer the case.

Signed-off-by: Simon McVittie <smcv@collabora.com>

Signed-off-by: Simon McVittie <smcv@collabora.com>

There is a race condition here between these chains of events, which as
far as I can tell has existed for at least 10 years:

* server receives Tests.Trigger() and schedules SignalTests.Triggered
* server returns to main loop
* server emits SignalTests.Triggered
* client receives SignalTests.Triggered

and

* server receives Tests.Trigger() and replies with success
* client receives success and emits SignalTests.Trigger
* server receives SignalTests.Trigger and calls CallbackTests.Response()
* client receives CallbackTests.Response() and calls Tests.Exit()
* server receives Tests.Exit() and replies with success
* client quits its main loop

If we don't reply to Tests.Trigger() until after the SignalTests.Triggered
signal has been sent, because the client called Tests.Trigger()
asynchronously, messages are not re-ordered and the reply arrives after
the signal; so the whole chain of events leading up to
"client receives SignalTests.Triggered" happens before
"client receives success and emits SignalTests.Trigger" and there is
no race condition.

Bug-Debian: https://bugs.debian.org/898158

Signed-off-by: Simon McVittie <smcv@debian.org>

Now that Python 2.6 isn't a supported version in Debian, it doesn't
get a gi module, but we can still get some minimal test coverage.

set() has been a built-in since 2.4, and we don't support older versions.