dogtail-devel Icons in sniff

[Dave Malcolm <dmalcolm redhat com>]

I've implemented icon support in 'sniff', based on the code in at-poke
(and copying the icons from there).

You can see a screenshot here:
http://people.redhat.com/dmalcolm/Screenshot-Sniff.png

I've committed the code to CVS.  

You'll need to update to the latest CVS pyspi when using this latest CVS
sniff, since I had to extend pyspi to do this (adding role support, as
opposed to role name).  Dogtail packages should have a dependency on
pyspi>=latest-pyspi version when they are released, to handle this kind
of thing.

I haven't attempted to add installation of the icons anywhere yet.

Once we have working libwnck bindings we ought to be able to get the
proper icons for each application, which will further help the usability
of sniff.