This adds code for a number of example graphs for use in tests of the aga
module.  They also demonstrate several different ways of constructing
graphs using the aga callbacks.

It adds one actual testcase, which just verifies that the example graph
look like what they're supposed to.  Specifically it computes a set of
adjacency lists for the example graphs from the callback code, then
compares that to a canned example of what it should be.
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>