[feature/prune-users] Rework user_delete() functions_user.php

user_delete now uses fewer queries to delete a set of users of size > 1 by
accepting an array of users rather than a single user at a time.  This required
changing the third parameter, however the function retains its former behavior
with the old-style parameters.

PHPBB3-9622
[feature/prune-users] Apply e6ed55a9c1ceb07ab2e87d4a53f9e688fda319c5.

This was done in PHPBB3-9872.

PHPBB3-9622
[feature/prune-users] Adjust some language strings for new features

Adjust two language strings for ACP prune feature to include descriptions for
new features.

PHPBB3-9622
Merge commit '441755bf170e49799e311c71b2123ff263970d62' into feature/prune-users

* commit '441755bf170e49799e311c71b2123ff263970d62':
  [ticket/9874] view_log() performs unneeded count query over all log entries.
Merge commit '47dc492839ea44cb9aa3d0ad23f09dd2fd0b4ed9' into feature/prune-users

* commit '47dc492839ea44cb9aa3d0ad23f09dd2fd0b4ed9':
  [ticket/9997] Fixed an inconsistency in the Moderator Control Panel
Merge commit 'e6ed55a9c1ceb07ab2e87d4a53f9e688fda319c5' into feature/prune-users

* commit 'e6ed55a9c1ceb07ab2e87d4a53f9e688fda319c5':
  [ticket/9872] Removed some useless code that broke delete_posts

These changes have already been applied in an earlier commit.
Therefore this commit is empty. Merge was done using 'ours' strategy.
[feature/prune-users] Apply 904bcb86a054ab6256da565098eb9bd8ab20414b.

This was done in PHPBB3-7834.

PHPBB3-9622
Merge commit '904bcb86a054ab6256da565098eb9bd8ab20414b' into feature/prune-users

* commit '904bcb86a054ab6256da565098eb9bd8ab20414b':
  [ticket/7834] Topic time didn't update when first post was deleted
Merge commit 'ee0db1a1d5f0150016d0971057f889f2366f9856' into feature/prune-users

* commit 'ee0db1a1d5f0150016d0971057f889f2366f9856':
Merge branch 'develop' into feature/prune-users

* develop: (170 commits)
  [ticket/10145] Always recompile all templates when DEBUG_EXTRA is defined.
  [feature/attachment-management-no-reassignment] Handle privacy and some more.
  [ticket/10148] Turn TEMPLATE_BITFIELD into an instance variable.
  [ticket/10147] Corrected a typo in includes/functions_template.php.
  [ticket/10141] Save a hash lookup when value is not in cache.
  [ticket/10143] Added tests for storing a previously deleted value in db cache.
  [ticket/10105] Update AIM express link.
  [ticket/10105] Update AIM application download link.
  [ticket/10137] Remove unintended space at end of PHP_URL_FOPEN_SUPPORT_EXPLAIN.
  [ticket/10141] Split double-assignment into conditional and unconditional part.
  [ticket/10141] Use a cache in $auth->_fill_acl() for better performance.
  [ticket/9961] Create log entries when users are activated.
  [ticket/10139] Make signatures of set_atomic() consistent by using $new_value.
  [ticket/10139] Rename $cache to $use_cache to avoid confusion with cache object
  [ticket/10006] Remove unneeded if statements
  [ticket/10006] Remove return values
  [ticket/10006] More testing
  [ticket/10006] Tweak the tests a bit
  [ticket/10006] Add phpbb_config::delete
  [ticket/7941] Added @return to generate_board_url docstring.
  ...
[feature/prune-users] Fixed whitespace in language file.

PHPBB3-9622
[feature/prune-users] Call sql_is_set for user ids once in user_delete.

PHPBB3-9622
[feature/prune-users] Replaced missed occurrences of $user_id with $user_ids.

PHPBB3-9622
[feature/prune-users] Call sql_is_set once for author ids in user_delete.

PHPBB3-9622
[feature/prune-users] Fixed user id check in undelivered users loop.

There is now $user_ids instead of one $user_id.

PHPBB3-9622
[feature/prune_users] Moved set_config_count out of user loop.

PHPBB3-9622
[feature/prune-users] Minor UI adjustment and bug fixes

Removed unneeded hidden fields in confirmation page.  Do not show group prune
dropdown if there are no groups, etc.

PHPBB3-9622
[ticket/8743] Include poster´s name in mail notifications

PHPBB3-8743
[feature/prune-users] Cosmetic changes per bantu's review.

PHPBB3-9622
[feature/dic] Convert common.php to Symfony2 DependencyInjection component

PHPBB3-10739