build script, bugfixes.

Added a build script that builds .class files and RMI stubs.

Tested with multiple workers, which uncovered the silly mistake I
previously made of running the watchdog synchronously. D'oh.

Added functionality to the worker server that makes it drop a certain
percentage of pings, to mock transient link failures. This uncovered a
NullPointerException if the first watchdog ping fails.

Also tested with more concurrent work requests than available workers,
which made me realize that the previous behavior of barfing when there
were no free workers was unacceptable. Fixed.