Phew ... Lots of debugging. This is the commit in which I
discovered AC/THC fails when it uses %rsp offsets instead of
%rbp offsets. And that we need to be careful with local variables
inside ASYNCs.

Anyway, this commit does the following:

    -- You can build for LAZY/EAGER using a configure flag:

            --enable-eager

       By default, it builds for lazy.

    -- Fix abort example to yield async 0. The print out result
       is quite interesting.

    -- Fix caller to use alloca, just to be paranoid about passing
       the local variable transaction_id. This is probably not
       necessary in this example, but it demonstrates the care
       required to pass locals in async's.