Drupal 7.23, 2013-08-07
-----------------------
- Fixed the default ordering of CSS files for sites using right-to-left
  languages, to consistently place the right-to-left override file immediately
  after the CSS it is overriding (API change: https://drupal.org/node/2058463).
- Fixed drupal_render() to always return an empty string when there is no
  output, rather than sometimes returning NULL (minor API change).
- Changed the password reset form to pre-fill the username when requested via a
  URL query parameter, and used this in the error message that appears after a
  failed login attempt (minor data structure and behavior change).
- Added human-readable labels to image styles, in addition to the existing
  machine-readable name (API change: https://drupal.org/node/2058503).

Drupal 7.22, 2013-04-03
-----------------------
- Fixed a bug which prevented empty HTTP headers (such as "0") from being set.
  (Minor behavior change: Callers of drupal_add_http_header() must now set
  FALSE explicitly to prevent a header from being sent at all; this was already
  indicated in the function's documentation.)
- Fixed entity argument not being passed to implementations of
  hook_file_download_access_alter(). The fix adds an additional context
  parameter that can be passed when calling drupal_alter() for any hook (API
  change: http://drupal.org/node/1882722).
- Fixed broken support for translatable comment fields (API change:
  http://drupal.org/node/1874724).
- Added a link to "Install another module" after a module has been successfully
  downloaded via the Update Manager (UI change).
- Added a link to the URL for running cron from outside the site to the Cron
  settings page (UI change).

Drupal 7.17, 2012-11-07
-----------------------
- Prevented duplicate HTML IDs from appearing when two forms are displayed on
  the same page and one of them is submitted with invalid data (minor markup
  change).
- Allowed aggregator feed items to have URLs longer than 255 characters
  (schema change which results in several columns in the Aggregator module's
  database tables changing from VARCHAR to TEXT fields).
- Added hook_taxonomy_term_view() and standardized the process for rendering
  taxonomy terms to invoke hook_entity_view() and otherwise make it consistent
  with other entities (API change: http://drupal.org/node/1808870).
- Changed the hook_menu() entry for Drupal's rss.xml page to prevent extra path
  components from being accidentally passed to the page callback function (data
  structure change).
- Fixed the theme settings form to properly clean up submitted values in
  $form_state['values'] when the form is submitted (data structure change).
- Fixed double occurrence of a "ul" HTML tag on secondary local tasks in the
  Seven theme (markup change).
- Fixed bugs which caused taxonomy vocabulary and shortcut set titles to be
  double-escaped. The fix replaces the taxonomy vocabulary overview page and
  "Edit shortcuts" menu items' title callback entries in hook_menu() with new
  functions that do not escape HTML characters (data structure change).
- Modified the node listing database query on Drupal's default front page to
  add table aliases for better query altering (this is a data structure change
  affecting code which implements hook_query_alter() on this query).

Drupal 7.15, 2012-08-01
-----------------------
- Changed the System module's hook_block_info() implementation to assign the
  "Main page content" and "System help" blocks to appropriate regions by
  default and prevent error messages on the block administration page (data
  structure change).
- Renamed the "Field" column on the Manage Fields screen to "Field type", since
  the former was confusing and inaccurate (UI change).
- Introduced generic entity language support. Entities may now declare their
  language property in hook_entity_info(), and modules working with entities
  may access the language using entity_language() (API change:
  http://drupal.org/node/1626346).
- Fixed issue where field form structure was incomplete if field_access()
  returned FALSE. Instead of being incomplete, the form structure now has
  #access set to FALSE and field form validation is skipped (data structure
  change: http://drupal.org/node/1663020).

Drupal 7.14 2012-05-02
----------------------
- Improve UX for machine names for fields (UI change).
- Fixed user picture not appearing in comment preview (Markup change).

Drupal 7.12, 2012-02-01
----------------------
- Fixed bug with DrupalCacheArray property visibility preventing others from
  extending it (API change: http://drupal.org/node/1422264).
- Fixed bug with handling of non-ASCII characters in file names (API change:
  http://drupal.org/node/1424840).