Tabs patch!

CHANGES
-------

 + Introduced tabs. First, we extended the menu system to support tabs. Next, a tab was added for every link that was (1) an administrative action other than the implicit 'view' (2) relevant to that particular page only. This is illustrated by the fact that all tabs are verbs and that clicking a page's tab leads you to a subpage of that page.

 + Flattened the administration menu. The tabs helped simplify the navigation menu as I could separate 'actions' from 'navigation'. In addition, I removed the 'administer > configuration'-menu, renamed 'blocks' to 'sidebars' which I hope is a bit more descriptive, and made a couple more changes. Earlier, we already renamed 'taxonomy' to 'categorization' and we move 'statistics' under 'logs'.

 + Grouped settings. All settings have been grouped under 'administer > settings'.

TODO
----

 + Update core themes: only Xtemplate default supports tabs and even those look ugly.  Need help.

 + Update contributed modules.  The menu() hook changed drastically.  Updating your code adhere the new menu() function should be 90% of the work.  Moreover, ensure that your modue's admin links are still valid and that URLs to node get updated to the new scheme ('node/view/x' -> 'node/x').

- Usability improvement: simplified the administration menu of the aggregator
  module.

- Fixed categorize not working under sources and category views.

- Made the recent news items page, the source pages and the categorization
  pages use pagers.  Removed the 'Items per page' setting and made Drupal
  remember news items much longer.

- Code improvements by JonBob.  Thanks again.

- Fixed feed status not being reset when items are removed.

- Various aggregator module improvements.  Modified patch by drumm.

- Added support for 403 handling.  Patch by JonBob.  As a side benefit,
  administrators will be able to define a custom 403 page, just as they
  can define 404 pages now.

  This needs to be documented in the "Changes since / migrating to ..."
  pages.

Truncate UTF-8 patch. Introduced a new function truncate_utf8() for chopping off strings at unsure locations, without risking incomplete UTF-8 data.

- System: the 404 setting instructions advise using 'node', this should be '' (redirecting the user to the front page without any message whatsoever is confusing)

- Patch by Steven: removed redundant permission checks.  These are no longer
  required thanks to the new 404 handling.

- Patch 5592 by Goba: let drupal_map_assoc() rule.  :-)

- Renamed CHANGELOG to CHANGELOG.txt for Windows uses.

- Fixed bug #5628: wrong timestamp in aggregator.  Patch by BartJ.

- Fixed bug in image parsing: caused 'Array' to be printed on the screen.

Patch 5287 by Stefan: multiline help texts should become inside a single $output.

- Patch 5330 by Adrian: PostgreSQL updates and fixes.

- Patch 5256: code improvements: theme('header') + theme('footer') -> theme('page').
  Patch by Gerhard.

- Reworked error/status reporting in the aggregator module to fix a bug.

 - Adds drupal_set_header() and drupal_get_headers().
 - Cache now stores custom headers.
 - Replace theme_head() with drupal_get_html_head(), added drupal_set_html_head().
 - Added RSS autodiscover links to node, blog and taxonomy pages.

- Removed some debug info.

Round 3 of aggregator improvements:

 - Added support for new tags:
   + Optinal feed image: <image> tag.
   + Dublin core dates: <dc:date> <dcterms:created>, <dcterms:issued>,
     <dcterms:modified>.
 - Usability improvements:
   + On the administration page, made the feed/bundle titles link
     to the feeds/bundles' pages.  On the feed/bundle's page, made
     the 'Last updated' field link to the administration page.
   + Moved the 'syndication' menu one level down.
 - Updated some content sensitive help.
 - Further improved themeability.
 - Fixed some invalid HTML.

 + Added some a new theme fucntions to the aggregator to make it possible to
   theme the aggregator page.
 + Removed the <table> and much hardcoded CSS as well as theme("box")-es.
 + Added the aggregator's theme functions to Doxygen's themeable group.
 + Added breadcrumb trails to the aggregator pages.
 + Updated the core themes to take advantages of the improved themeability.

Screenshot:

 http://buytaert.net/temporary/aggregator-makeover.jpg

- Many excellent news aggregator improvements by Kjartan:
    + Added drupal_http_request().
    + Replaced rssfeeds with OPML feed subscription list.
    + Added support for pubDate.
    + Added support for conditional gets using ETag and Last-Modified.

- Added proper access checking to block and menu items.

/**
 * Wrapper around xml_parser_create() which extracts the encoding from the XML
 * data first and sets the output encoding to UTF-8. This function should be
 * used instead of xml_parser_create(), because PHP's XML parser doesn't check
 * the input encoding itself.
 *
 * This is also where unsupported encodings should be converted.
 * Callers should take this into account: $data might have been changed after
 * the call.
 *
 * @param $data The XML data which will be parsed later.
 */

Committed filter separation patch: all filter-related things are now in filter.module (which is a required module).
To do this cleanly, I reorganised some bits of system.module: there is now a generic handler available for simple variable-get/set based configuration pages. Look at filter_admin() or system_view() for example usage.

(based on the patch by Goba)

(sorry last commit, I promise :P)