[CJ][84236214] Allow dynamic reconfiguration

The immediate cause for this is to enable reloading at the REPL when only the configuration files have changed (thus the `defconfig` vars
don't get reloaded). However, this also opens the door for features like distributed configuration.

If this looks OK I can cut a 0.3.3 release.
i don't understand why we're accessing "OHAI" instead of foo, though i beliebe that's orthogonal to this test.