Here : http://www.actel.com/products/pa3/index.aspx is the link to all PA3/E files you can download without any points.
Pay attention to the "Using Global Resources in Actel ProASIC3/E Devices" Application Note, close to the bottom of the page. You'll find the description of global clock structure in that AN and in some of the files on the Actel's page.
Rgds, yego
P.s. Actually global clock is a mixture of a global backbone and some "local" ribs used to route your clocks all over the fpga. You can use both of them for clock routing, or use local ribs for general purpose routing.