Integrate __AFL_INIT into the weak-attributed default main function

[pgoodman]

[agroce]

Should we do persist-mode -- #143 -- instead? Seems like a good no-fork fit for our setting.

[agroce]

Or support both with two deepstate libraries to link to, in case someone wants to use tests that don't behave well under persist (in which case they need AFL, since libFuzzer is probably hosed)

[agroce]

well, less-fork, not no fork, but close enough