Major code tidy.

answertests.php

caschat.php

db/upgrade.php

deploy.php

doc/en/Authoring/Authoring_quick_start.md

doc/maintenance.php

edit_stack_form.php

healthcheck.php

lang/en/qtype_stack.php

locallib.php

question.php

questiontestrun.php

stack/answertest/at_general_cas.class.php

stack/answertest/atdecplaces.class.php

stack/answertest/controller.class.php

stack/cas/cassession.class.php

stack/cas/casstring.class.php

stack/cas/castext.class.php

stack/cas/connector.class.php

stack/cas/connector.server.class.php