Run hook_boot for installed modules on setUp()

Currently DrupalWebTestCase::setUp() is installing modules and then running tests on the same request.

It is also performing a run cron after the installation, so if some module implement hook_cron()(i.e. versioncontrol) and need to use one of its dependencies feature during it(i.e. dbtng autoload register during dbtng_boot()) it produces errors.

Naturally this happens only when you have not installed the module with the hook_boot() on the drupal running simpletest, because if it has it installed, the initial bootstrap before getting into setUp() method will trigger the invocation for the simpletest run. This i.e. happens on drupal.org testbots, and that's why i.e. versioncontrol tests does not run for 6.x-2.x

I'll add a patch just after this post.