genmon plugin for the Xfce panel

The genmon plugin is a 'generic monitor' plugin that cyclically spawns
a script or program and captures its output, then displays the resulting 
string in the panel.  It can be used to display a picture, a bar, tooltip, 
and/or a button, so it can be used to display various information about 
the system, such as temperature, processor speed, battery level, etcetera...
