dirstate: wrap setparent calls with begin/endparentchange (issue4353) This wraps all the locations of dirstate.setparent with the appropriate begin/endparentchange calls. This will prevent exceptions during those calls from causing incoherent dirstates (issue4353).

dirstate: add begin/endparentchange to dirstate It's possible for the dirstate to become incoherent (issue4353) if there is an exception in the middle of the dirstate parent and entries being written (like if the user ctrl+c's). This change adds begin/endparentchange which a future patch will require to be set before changing the dirstate parent. This will allow us to prevent writing the dirstate in the event of an exception while changing the parent.