The problem with using include is that when the file that is loaded
does not contain the plugin class (e.g. because the directory name is
wrong), the file could be loaded again when the plugin class is
requested a second time which will lead to a fatal error because of
class redeclaration.

This partially reverts de50cad6 as the
strict check breaks existing plugins and this shouldn't be changed
without prior discussion and a warning for plugin authors with some time
to adjust their plugins. Now all characters that are valid in PHP class
names except "_" are allowed.

This adds more tolerance to the width calculations of the media manager
panes which avoids that the right pane is displayed below the other
panes.

Before this change it was possible to send arbitrary HTML content to
subscribers, if you are using HTML subscription mails and have
untrustworthy editors, it is recommended to upgrade as soon as possible
(this doesn't affect the current stable release).

This displays an error message when building the plugin list and an
enabled plugin does not follow the plugin naming conventions. This
should help plugin developers and admins understand why their plugins
aren't working.

When loading plugins, $lang might not be initialized yet, so use a
hardcoded error message instead, especially as this error should only be
displayed for the admin (and then fixed). This also removes the
previously localized message, it might be re-added as part of the new
extension manager.

This checks if plugin names are valid and only loads valid plugin files,
this could prevent some errors from wrong upgrades as described in
FS#2464.

The BOM at the beginning of some plugin.info.txt files prevented the
plugin manager from correctly reading the base property and thus it
installed the plugin in the wrong directory.

update the url to the latest one used in the manager (FS#2463)

This fixes the test for existing subscriptions by not only testing if
the subscription for the deepest namespace level is for the current page
but by simply testing all levels. Test case is included, it fails
without this change.

FIX for FS#2463 <https://bugs.dokuwiki.org/index.php?do=details&task_id=2463>

this function was removed in PHP 5.4.0

The class loader isn't available at that place in inc/init.php so the
check if the sitemap is compressed didn't work.