refetch state after preSave listener in unit of work. if state changes in preSave listener it is not taken into concideration when an object is saved/deleted etc. also fixed some small stuff in tests and added new coverage report

refactored test harness and moved logic away from the run.php file. fixed coverage reporting so that it now generates a full html coverage files. look in tests/coverage/index.php in a browser for details

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Fixed a bug in the nestedset implementation. When using single table inheritance all node instances need to use the same tree object. previously every subclass created it's own tree object which resulted in strange behaviour.

Not using User model since users gets its table cleared before each
test method call ($this->objTable()->clear()), and that affects the
result