rename plugin main class files

classes/pluginhost.php

plugins/af_explosm/init.php

plugins/af_gocomics/init.php

plugins/af_pennyarcade/init.php

plugins/af_redditimgur/init.php

plugins/auth_imap/init.php

plugins/auth_internal/init.php

plugins/auth_remote/init.php

plugins/digest/init.php

plugins/example/init.php

plugins/example_feed/init.php

plugins/example_routing/init.php

plugins/flattr/init.php

plugins/googleplus/init.php

plugins/identica/init.php

plugins/import_export/init.php

plugins/instances/init.php

plugins/mail/init.php

plugins/note/init.php

plugins/owncloud/init.php