move back to having relativePath in the pom for the parent.

this is necessary in order to get a build on a machine that has never
built before to work.
move exhaustive tests to their own package.

Alas, with the decision to separate the integration tests into a
different jar, and signing jars, we run into a java exception if I use
io.humble.ferry as the package name for these tests.

The unfortunately side effect of this is I have to make a
package-private member of JNIMemoryManager public.