(e.g. admin.module was removed -> needs menu cache update).

- Patch #14731 by chx: made it possible to rewrite node queries.

- Patch #15570 by Drumm: integrated the admin and system module.  Renamed the callback as per Goba's suggestion.

- Patch #15337 by Gerhard: fixed bug in upgrade path.  The 'update_start' variable got corrupted.

Making the installation instructions a bit clearer for newbies and it explicitly explains that the commands are for the command line.

- Fixing broken "pagerank" detection

- Renamed 'visit' to 'view'.

- Watchdog improvement: added a 'view' link for 'access denied' messages.

- Patch #15399 by adschar: fixed PHP5 error when a new session is inserted into the session table. (Better fix.)

- Patch #15399 by adschar: fixed PHP5 error when a new session is inserted into the session table.

  We added a 'severity' column to watchdog():
    watchdog($type, $message, $link) --> watchdog($type, $message, $severity, $link);

    * Specify a severity in case you are reporting a warning or error.
    * The $link-parameter is now the fourth parameter instead of the third.

  TODO: document this in the upgrade guide.