Fixes #1480

In an older version of PHP a file_exists() call would issue a warning
when the file did not exist. This was fixed in later PHP releases. Since
we require PHP 5.3 now, there's no need to supress any error here
anymore. This might even give a minor performance boost.

This resolves issues with broken images when the wiki feed is
hosted by third parties (e.g. FeedBurner), as mentioned in
FS#2931 comments.

Revert "Exclude hidden pages (config["hidepages"]) from RSS feed (see https://www.dokuwiki.org/config:hidepages)"

This reverts commit f5151bdb.

This reverts commit a010fc32.

Exclude hidden pages (config["hidepages"]) from RSS feed (see https://www.dokuwiki.org/config:hidepages)

FS#2738, fix double encoding of html entities in RSS feeds (updates feed.php for changes to Diff class introduced in PR#179)

Before this change the last modification time was taken from metadata
and then the revision that was specified there was loaded from the
attic. Now revisions from attic are only loaded when the page has been
modified more recently and the date is normally the last modification
time of the page source. This was a problem when the most recent change
was an external edit, then an older revision was shown in the feed.

This fixes the problem that media items in the feed got the title of the
previous item when useheading was enabled as no metadata is loaded for
media entries and thus the previous metadata was used again. This also
fixes dates for media files.

this should avoid false positive matches on user content (which is
already escaped at this point)

can someone with better regex skills please revise this?

The function tpl_getFavicon() was doing more than its name was implying. Therefore the new tpl_getMediaFile() was introduced (which is doing nearly exactly the same) and tpl_getFavicon() was deprecated.
tpl_favicon() can still be used, though.

  * Do not emit E_NOTICEs
  * Introduce explicit feed mode default value »recent« instead of handling
    every unknown feed mode as recent changes mode. This means:
    - FEED_MODE_UNKNOWN is only executed if the given feed mode is indeed
      unknown. This is specifically not the case if no feed mode request param
      has been specified or the requested feed mode is »recent«.
    - FEED_MODE_UNKNOWN dies with an error as default behaviour
  * opt[items] is forced to be a non-negative integer
  * opt[show_minor] is forced to be a boolean and thus has a default value of
    false instead of null

As of VIM 7.3 it is no longer possible to specify the encoding in the
modeline. This gives an error message whenever such a file is opened,
thus this commit removes the enc setting from the modeline.