Now classes and data- attributes can be added to individual options

Since Firebug it is no longer necessary to structure html with linebreaks. See also Issue #924

as pointed out in
https://github.com/splitbrain/dokuwiki/pull/1530/files/b89dfc20f1e13333ce49ce0d6a3a83cc9836094b#r60392099

Caching must differentiate between a call with $ascii == true and a call
without that parameter. Since calling that function with $ascii == true
rare, we simply do not cache that case.

This `$conf['pluginmanager']` setting was especially for disabling of
pluginmanager in farms. (see also commit c45608df )

remaining folders with .disabled in the foldername are displayed in
extension manager with rename warning.

This adds the possibility to define file with protected users in the
config cascade to be used with the plain auth mechanism.

This makes it possible for farms to have way to inherit Farmer users in
animals.

Close #1323

The function wikiFN effectively takes the $clean flag now into account when
caching filepaths and when returning them from cache.

Fixes #1536

Textareas use CRLF, but internally we use LF.

As suggested by @micgro42 the plugin namespace should use a vendor
prefix to avoid name clashes when DokuWiki is integrated with other
software.

@scrutinizer-notifier noticed that the $pageid might be false when
page_findnearest looks for it.

As in wikiFN cleaning the id should be optional, but still the default, in mediaFN as well.

when a form was submitted with an empty input, that data should still
overwrite the preset value.

This is a security measurement supported in Chrome and Opera (and
probably other browsers soonish)

See http://mathiasbynens.github.io/rel-noopener/ for rationale

This introduces an autoloader for namespaces starting with plugin\*

This way, plugins can easily have additional classes auto loaded without
needing to register their own loader. A plugin\*\test\* namespace will
automatically be mapped to the _test directory of the plugin.

This adds 3way merge functionality to our DifferenceEngine stack. The
code was taken from the PEAR Text_Diff3 package and adapted to work with
our implementation.

For the curious:
Here's a short Origin tree of the different versions of the Diff code to
make clear how our implementation is related to the PEAR package.

-- original code Geoffrey T. Dairiki
   `-- Adaption for the Horde project
       |-- Adaption for phpwiki
       |   `-- Adaption for MediaWiki
       |       `-- Adaption for DokuWiki
       `-- Creation of PEAR Text_Diff

This should fix the test problems errors in #1527. When requesting a
HTTPS URI from a HTTP only proxy, the initial connection is *not* TLS
secured. The URI scheme is only relevant when directly connecting.

This also changes the (wrong) assumption that everything on port 443 is
always TLS secured. Only the URI scheme should decide that.

This is to ensure that we use SSL/TLS if a custom port is defined an no
proxy is used.

Fixes #1526

The header() method of PHP is vulnerable to HTTP Response Splitting
attacks.

This change makes sure the URL passed to send_redirect (and thus to
header()) does not contain any control characters that would be needed
to execute such an attack.

Cleaning input is recommended anyway.