[ticket/10605] Check for orphan privmsgs when deleting a user

Also moved the hole code into a new function.

PHPBB3-10605
[ticket/9089] Add tabindex to PM recipient box, to allow tabbing to the subject

I also added tabindex 1 to the buttons for adding the recipients.
Also note, that duplicated tabindex are fine:
http://www.w3.org/TR/html4/interact/forms.html#adef-tabindex

PHPBB3-9089
[ticket/10605] Delete orphan private messages on update

PHPBB3-10605
[ticket/9089] Add tabindex to pm/topic/post icon-options aswell

PHPBB3-9089
[ticket/10605] Prefix function with phpbb_ and use true instead of 1

PHPBB3-10605
[ticket/8743] Include poster´s name in mail notifications

PHPBB3-8743
[ticket/10605] Use unset() instead of checking user_id over and over again.

PHPBB3-10605
[ticket/10605] Turn $undelivered_user into a real array of counters.

PHPBB3-10605
[ticket/10605] Remove unused variable declarations.

PHPBB3-10605
[ticket/10605] Remove unnecessary array_keys calls on $delete_rows.

PHPBB3-10605
[ticket/10605] Remove unnecessary $delete_ids array.

PHPBB3-10605
[ticket/10605] Break long comment into multiple lines 80 chars short.

PHPBB3-10605
[ticket/10605] Rename $delete_rows to $delete_ids.

PHPBB3-10605
[ticket/10605] Split query to be able to use indexes

PHPBB3-10605
[ticket/10605] Reset user´s pm count to 0 when deleting his PMs

PHPBB3-10605
[ticket/10605] Fix syntax error in database updater.

PHPBB3-10605
[ticket/10605] Add a section for updating from 3.0.10 to schema updates.

Without it data updates do not appear to be run.

PHPBB3-10605
[ticket/10605] Fix left join usage.

Previously this produced broken SQL:

SELECT p.msg_id FROM phpbb_privmsgs p
LEFT JOIN 0 phpbb_privmsgs_to ON (p.msg_id = t.msg_id)
WHERE t.user_id IS NULL LIMIT 500 OFFSET 0

PHPBB3-10605
[ticket/10661] Added &nbsp; to enumerated recipients (prosilver)

Added missing &nbsp; to enumerated recipients after IF statements
to see if it is a group or not (to_recipient.IS_GROUP and
bcc_recipient.ISGROUP), in posting_editor template in prosilver
style.

PHPBB3-10661
[ticket/10605] Add parameter documentation to phpbb_delete_user_pms

PHPBB3-10605