FS#3526 - Add option to disable BIND zone check (the intention for the feature request was more to hide log-messages and not to disable the named-checkzone-call)

Added prefetching to dovecot to halve database-queries
Added mdbox-creation for new Mailboxes in mdbox-format

Conflicts:
	install/tpl/debian6_dovecot-sql.conf.master
	install/tpl/debian_dovecot-sql.conf.master
	install/tpl/debian_postfix.conf.master
	install/tpl/fedora_dovecot-sql.conf.master
	install/tpl/fedora_postfix.conf.master
	install/tpl/gentoo_postfix.conf.master
	install/tpl/opensuse_dovecot-sql.conf.master
	install/tpl/opensuse_postfix.conf.master
	interface/web/admin/templates/server_config_mail_edit.htm
	server/cron_daily.php
	server/plugins-available/mail_plugin.inc.php
	server/plugins-available/postfix_server_plugin.inc.php

see:
- http://git.ispconfig.org/panders/ispconfig3/commit/f7ec00b2f8ba3efc5bdeacef9c813f8a826ae3be#note_453
- http://git.ispconfig.org/panders/ispconfig3/commit/f7ec00b2f8ba3efc5bdeacef9c813f8a826ae3be#note_452
- http://git.ispconfig.org/panders/ispconfig3/commit/f7ec00b2f8ba3efc5bdeacef9c813f8a826ae3be#note_450
- http://git.ispconfig.org/panders/ispconfig3/commit/f7ec00b2f8ba3efc5bdeacef9c813f8a826ae3be#note_449

- http://en.wikipedia.org/wiki/SPDY

- Directive snippets can now be made available to clients; clients can select an available directive snippet for a website - the appropriate snippet will then be written to the vhost configuration file. This is useful for example on nginx where clients have no access to the Options tab of a website.

- Added HHVM to "Default PHP Handler" field (server configuration).
- Fixed "Unable to load the server configuration from database." error when running server.sh.
- Fixed Javascript (accordions weren't working anymore, directive snippets and other placeholders couldn't be added anymore).

-Added a new option "Network Filesystem" under System > Server config > Web to toggle on / off the _netdev option for the bind mounts in /etc/fstab

Use dovecot or maildrop in default-cases
Switching to LMTP and back included in server-postfix-plugin
validator added to disable switching uid-mapping when already created mailusers or in multiserver-environment

- Merged language files

Removed backup_dir_mount_cmd option from Sysstem > server config. The option has been replaced by a script /usr/local/ispconfig/server/scripts/backup_dir_mount.sh. If this script exists, is exacutable and is owned by the root user, then it will be executed upfront of the backup jobs when the option "Backup directory is a mount?" is enabled in server config settings.