#176805 by dww: conditional linking to dblog pages in update.php, so if the module is not enabled, we don't get broken links

#162432 by bjaspan and chx: serial columns need their keys defined in db_change_field() and friends in MySQL

#171646 by JirkaRybka: store version usage information for every source string, optimize caching and prune the initially unused strings

#170638 by JirkaRybka and chx: move update access variable to settings.php, so we can check whether it is wide open, and we have one place for settings

#154949 by Crell and dww: let modules and themes specify a minimum required PHP version, under which they will not be possible to be turned on

- Patch #146910 by dww: only allow enabling modules with the same Drupal core compatibility version.

- Patch #137211 by merlinofchaos: move theme information to .info files and improved theme inheritance.

#127539: progressive operation support, refactoring update.php code to a generic batch API to support runnning operations in multiple HTTP requests
  - update.php is already on the batch API
  - node access rebuilding is in the works
  - automatic locale importing is in the works

 Thanks to Yves Chedemois (yched) for the good code quality, very wide awareness of issues related to batches,
 and the fantastic turnaround times. Hats off.

- Refactor partial-page handling for the maintenance page. It's an exotic quirk for update.php and belongs there.

#100516: CSS preprocessor to cache and compress all .css files. Benchmarks show up to 40% faster page loads.

- Patch #77919 by chx, eaton, moshe, et al: enable programmaticaly submitted forms via the pull model.

- Keep all JS widget css together