Fix an uninitialized-pointer bug.

I should have caught this earlier. Calling runGame() without first
calling setLog(NULL) would lead to use of the uninitialized "log_"
pointer. This is now fixed.
Add a much better "main.cc" harness.

The run_FooBot harness now comes with command-line argument parsing:
you can pass "--quiet" to suppress the initial logging spew, or
"--players", "--games", or "--every" to affect the number of players,
total number of games played, and frequency of statistical spew,
respectively.