evolve: fixed lock acquire before checking state Before checking the states `repo.lock()` and `repo.wlock()` need to be acquired. This was not happening in `evolve()` earlier. This patch creates a seperate `_performevolve()` funtion which can be then called with locks acquired. This also removes the redundant lock acuquiring of `abortevolve` and `continueevolve` as lock is now taken earlier.