test suite could check for memory leaks

[davepacheco]

The test suite has several tests that use gcore to save a core file, then open mdb on that core file, load mdb_v8, and run a bunch of dcmds. They should probably also save a core file of mdb and run findleaks on that to make sure we're not leaking memory.

As part of this, we'll probably want to commonize the code that does all this, since it's currently replicated in several places.

[davepacheco]

For reference, I added a facility under #101 to run findleaks on mdb after running each test, but it doesn't automatically look for new leaks or anything.