Domain object events possible bug

Hey Lox,

I think I may have found a bug in how DomainObject events are triggered.

It looks like DomainObjects returned from finder methods aren't triggering methods such as `afterUpdate` when they're being saved.

This pull request just includes a test case to reproduce the behaviour. I'll continue looking into the cause and hopefully post a fix soon :-)

PS. This will need some tidying up before including in mainline Pheasant. Please don't merge this yet. Where would be the best place to put this test case by the way? Is DomanObjectTest appropriate? I'll need to move the `Blah` class elsewhere too...