we should add an alarm function to automatically fail tests that take more than a certain amount of time to run (on the assumption that they've deadlocked).

something on the order of a minute is probably fine.

i think the best way to do this would be to spin up a dedicated thread that sits around waiting for time to pass.  once enough time passes, it can abort the process.

i specifically don't think that we should try to use gmaincontext to do this because some tests still fork, and forking after gmaincontext is up is not safe.

it should be possible for individual tests to adjust the timeout (for performance tests) or for the environment to do it, either via environment variable or commandline switch (to facilitate 'make check' on very very slow builders).