Internet Explorer 8 (and maybe others) seem to use different
capitalization in the ACCEPT_CHARSET header between "normal" requests
and AJAX requests. This causes a browser UID mismatch and thus an
unecessary reauthentication.

Replaced it by the old tpl_include_page() and made it more flexible by adding a boolean $propagate parameter.
(It's false by default for backwards compatibility reasons. Should it rather be true? That would probably be what most users want.)

This problem was reported in https://forum.dokuwiki.org/thread/8143.
Apart from warnings you could notice that when you have namespaces "foo"
and "f.o" and you open the sitemap for "foo" that "f.o" is opened, too.

this is a temporary and somewhat ugly fix. digest subscriptions should
make use of the inline format just as the 'every' subscriptions do.
But it makes sense to implement it correctly in the subscription branch
instead and not introduce new code in the RC.

The link doesn't exist in the English version and it doesn't work
anymore because appending a parameter to a link doesn't work when the
link is not just a URL but an HTML link

This fixes error messages about invalid plugin names for directories in
the plugin directory which didn't contain any plugin. Now the message is
only displayed for plugins which couldn't be loaded because of the
invalid name.

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.

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.

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.