Added test for autoload issue observed with BioRuby tests on JRuby.

Many BioRuby unit tests fail on JRuby when run as a suite; this adds a minimal test case for the root cause of that problem.

Specifically, on JRuby but not MRI, when:
* a module creates an autoload entry
* a file which would be loaded by that entry is instead loaded by directly invoking require
* the autoload entry is set up again with another call to the parent module's #autoload method

Then subsequent access to the child module fails with "NameError: uninitialized constant ..."