add a a halui jogging test

This test checks jogging via halui.

The test stands up a full simulated linuxcnc instance, including halui
and a custom [DISPLAY]DISPLAY "ui" written in python.

This python "UI" uses the linuxcnc python module and the hal python
module.  It creates some HAL pins, which are netted to halui (for
commanding) and motion (for feedback).

The python UI pokes halui's pins to select joints and to jog in the plus
and minus directions, and monitors motion's axis.N pins to verify that
the correct jogs happened.
use "modern" gtk refcounting api

This changes classicladder's pixbuf handling to use GTK's more modern
refcounting API.

gdk_pixbuf_unref() has been deprecated since 2.0:

    https://developer.gnome.org/gdk-pixbuf/2.22/gdk-pixbuf-refcounting.html

The oldest distro we actively support is Hardy, which has GDK 2.12,
so we're ok here.
fix a typo in halui manpage
halui manpage: document the mdi-command-XX pins