[ticket/11259] Make phpbb_admin_path available everywhere

PHPBB3-11259
[ticket/11259] Also make adm_relative_path available in the container

PHPBB3-11259
[ticket/11259] adm_relative_path -> phpbb_adm_relative_path

We can assume they properly format their config settings, right?

PHPBB3-11259
[ticket/11259] htmlspecialchars($phpbb_admin_path)

PHPBB3-11259
[ticket/11283] Extension manager follow symlinks.

All extensions are located in the `phpBB/ext` directory,
however the `phpbb_extension_manager::all_available()`
method only looks into actual directories and ignores symlinks.

Add the `RecursiveDirectoryIterator::FOLLOW_SYMLINKS` flag to
the `new RecursiveDirectoryIterator` call so that you can store
extensions in a different location and use symlinks so that
phpBB can recognise them.

PHPBB3-11283
[ticket/11291] phing: Make sure composer is available before calling it.

Older versions of the tree didn't use it.

PHPBB3-11291
[ticket/11292] Fix: Newlines removed in display of PM reports

Report text is run through make_clickable and bbcode_nl2br for PMs
just as it is for posts.

PHPBB3-11292
[ticket/11037] Eliminate globals from cache service.

PHPBB3-11037
[ticket/11293] Add a note that mysqli should be in front of mysql.

php 5.5 alpha 2 deprecated mysql extension, prefer mysqli if
both are available.

PHPBB3-11293
[ticket/11037] Add/update docblocks.

PHPBB3-11037
[ticket/11037] Update services.yml.

PHPBB3-11037
[ticket/11291] phing: Correct dependencies of composer target.

This command runs composer in the phpBB tree and does not write to the build
folders. Thus, it does not have to depend on prepare and clean targets.

PHPBB3-11291
[ticket/11291] phing: Add --dev to composer install.

The composer target runs composer in the phpBB tree in order to load
dependencies for testing. The testing framework may have additional
development dependencies (e.g. goutte). We also have to load those.

PHPBB3-11291
[ticket/11291] phing: Add description for composer target.

PHPBB3-11291
[ticket/11291] phing: Adjust directory format of composer exec.

Adjust the directory format to what all the other exec calls are using.

PHPBB3-11291
[ticket/11291] phing: The package target does not depend on composer.

The packaging process does not require running composer in the phpBB tree.
It does however require running composer on the git exports, but this is not
what the composer target does.

PHPBB3-11291
[ticket/11291] phing: Remove no longer needed create-package target.

PHPBB3-11291
[ticket/11291] phing packaging: Export composer.phar and install dependencies.

PHPBB3-11291
[ticket/11291] phing: Exclude vendor folder from diffs.

Otherwise we end up with very huge diffs and the build process is severely
slowed down.

PHPBB3-11291
[ticket/11291] phing: Add checkreturn="true" to all new commands.

PHPBB3-11291